diff --git a/README.md b/README.md
index 91d56e141..c2034e4c5 100644
--- a/README.md
+++ b/README.md
@@ -178,7 +178,7 @@ from = "onboarding@resend.dev"  # the sender; default onboarding@resend.dev, whi
 dir = "~/.thirdshift/logs"   # where session logs go; default ~/.thirdshift/logs
 ```
 
-Every key holds its real value, so a Run reading it does exactly what it does with no file. `email.to` has no default, so it is the only line written commented out. `setup` asks nothing, prints the file's path on stderr and exits `0` with stdout empty. A User config that is already there keeps its values; one a Run would refuse is refused the same way, exit `1`, and not touched. Any argument after `setup` is an argument error (exit `2`).
+Every key holds its real value, so a Run reading it does exactly what it does with no file. `email.to` has no default, so `setup` suggests one: the public email of your GitHub profile (from `gh api user`), else your global git `user.email`, unless that is a `@users.noreply.github.com` address, which can't receive mail. With neither, `email.to` is the only line written commented out, as above. `setup` never asks `gh` for more scopes, so a private GitHub email is not read, and a Run never looks the suggestion up: `--email` with no address and no `email.to` still stops the Run. `setup` asks nothing, prints the file's path on stderr and exits `0` with stdout empty. A User config that is already there keeps its values; one a Run would refuse is refused the same way, exit `1`, and not touched. Any argument after `setup` is an argument error (exit `2`).
 
 With `merge.always = true`, `thirdshift <Issue URL>` is a Merge run, and `thirdshift --no-merge <Issue URL>` (or `no-merge`, before or after the URL) leaves that one Run's pull request ready for review.
 
diff --git a/src/config.rs b/src/config.rs
index 84d2638af..8c4e19d15 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -7,6 +7,8 @@ use std::path::{Path, PathBuf};
 use anyhow::{Context, Result, anyhow, bail};
 use toml::{Table, Value};
 
+use crate::git::Git;
+use crate::github;
 use crate::notification::NotificationAsk;
 use crate::run::Goal;
 
@@ -133,8 +135,9 @@ impl EmailSettings {
 }
 
 /// Setup with no terminal: write the User config with every setting at its
-/// default, asking nothing. An existing User config keeps its values, once it
-/// parses as a Run would parse it, so Setup never resets a configured machine.
+/// default, asking nothing, and `email.to` as the suggested address, if there
+/// is one. An existing User config keeps its values, once it parses as a Run
+/// would parse it, so Setup never resets a configured machine.
 pub fn setup() -> Result<String> {
     let (home, path) = home_and_path()?;
     match std::fs::read_to_string(&path) {
@@ -151,7 +154,7 @@ pub fn setup() -> Result<String> {
         }
     }
     std::fs::create_dir_all(home.join(".thirdshift"))
-        .and_then(|()| std::fs::write(&path, DEFAULTS))
+        .and_then(|()| std::fs::write(&path, with_email_to(suggested_address(&home))))
         .with_context(|| format!("can't write {}", path.display()))?;
     Ok(format!("wrote the User config {}", path.display()))
 }
@@ -174,6 +177,36 @@ from = "onboarding@resend.dev"  # the sender; default onboarding@resend.dev, whi
 dir = "~/.thirdshift/logs"   # where session logs go; default ~/.thirdshift/logs
 "#;
 
+/// The line `DEFAULTS` holds for `email.to`, which has no default.
+const NO_EMAIL_TO: &str = r#"# to = "you@example.com"        # where email goes when the command names no address; no default"#;
+
+/// `DEFAULTS` with `email.to` set to `to`, if there is one.
+fn with_email_to(to: Option<String>) -> String {
+    let Some(to) = to else {
+        return DEFAULTS.to_string();
+    };
+    let (_, comment) = NO_EMAIL_TO.split_once("  # ").unwrap();
+    let line = format!("to = {}", Value::String(to));
+    DEFAULTS.replace(NO_EMAIL_TO, &format!("{line:<31} # {comment}"))
+}
+
+/// The address Setup suggests for `email.to`: the public email of the user's
+/// GitHub profile, else the global git `user.email`, unless that is a
+/// `@users.noreply.github.com` address, which can't receive mail. Only Setup
+/// looks it up; a Run never falls back to it.
+fn suggested_address(home: &Path) -> Option<String> {
+    let github = github::profile_email().ok().flatten();
+    github.filter(|email| !email.is_empty()).or_else(|| {
+        let git = Git::new(home).run(&["config", "--global", "user.email"]);
+        git.ok().filter(|email| {
+            !email.is_empty()
+                && !email
+                    .to_ascii_lowercase()
+                    .ends_with("@users.noreply.github.com")
+        })
+    })
+}
+
 /// `$HOME`, and the User config's path under it.
 fn home_and_path() -> Result<(PathBuf, PathBuf)> {
     let home = std::env::var_os("HOME")
@@ -219,6 +252,25 @@ mod tests {
         assert_eq!(config, UserConfig::defaults(Path::new("/home/me")));
     }
 
+    #[test]
+    fn a_suggested_address_sets_email_to_in_place_of_the_commented_out_line() {
+        assert!(DEFAULTS.contains(&format!("\n{NO_EMAIL_TO}\n")));
+        assert_eq!(with_email_to(None), DEFAULTS);
+        let text = with_email_to(Some("o\"brien@example.com".to_string()));
+        let config = parse(&text).unwrap();
+        assert_eq!(config.email.to.as_deref(), Some("o\"brien@example.com"));
+        let line = text.lines().find(|line| line.starts_with("to = ")).unwrap();
+        let from = text
+            .lines()
+            .find(|line| line.starts_with("from = "))
+            .unwrap();
+        assert_eq!(
+            line.find(" # "),
+            from.find("  # ").map(|at| at + 1),
+            "{text}"
+        );
+    }
+
     #[test]
     fn merge_always_is_read() {
         assert!(parse("[merge]\nalways = true\n").unwrap().merge_always);
diff --git a/src/github.rs b/src/github.rs
index fc8d0cd30..0813c8da5 100644
--- a/src/github.rs
+++ b/src/github.rs
@@ -1,4 +1,5 @@
-//! Asking GitHub, through `gh`, about issues and pull requests.
+//! Asking GitHub, through `gh`, about issues, pull requests and the signed-in
+//! user.
 
 use std::fmt;
 use std::process::Command;
@@ -52,6 +53,14 @@ pub fn close_issue(issue: &IssueUrl, comment: &str) -> Result<()> {
     ])
 }
 
+/// The public email of the signed-in user's GitHub profile, or `None` if it
+/// is private. Private addresses need the `user` scope, which a default
+/// `gh auth login` token lacks, so thirdshift never asks for them.
+pub fn profile_email() -> Result<Option<String>> {
+    let json = gh_json(&["api", "user"])?;
+    Ok(json["email"].as_str().map(str::to_string))
+}
+
 const PR_FIELDS: &str = "number,url,state,headRefName,baseRefName,isDraft";
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
diff --git a/tests/fakes/gh b/tests/fakes/gh
index ed85031ea..aceedc778 100644
--- a/tests/fakes/gh
+++ b/tests/fakes/gh
@@ -15,7 +15,8 @@ State lives in the JSON file named by $FAKE_GH_STATE:
      "on_merge"?: {"times", "script"},
      "refuse_merges"?: {"times", "error"},
      "after_merge"?: "<script>",
-     "failing"?: ["<command> <subcommand>", ...]}
+     "failing"?: ["<command> <subcommand>", ...],
+     "user_email"?: "<address>" | null}
 
 `gh pr merge` makes a real merge commit of the PR's head into its base in the
 bare origin repo beside $FAKE_GH_STATE (`origin.git`), whose HEAD names the
@@ -28,6 +29,9 @@ merged. Its `closingIssuesReferences` are the issues its body closes.
 
 An issue's title is its entry in `titles`, else `Issue <number>`.
 
+`gh api user` answers with the signed-in user's profile, whose public `email`
+is `user_email`, else null. `gh fake fails 'api user'` makes it fail.
+
 `gh issue close` closes the issue, recording its `--comment`; on an issue
 already closed it only warns, as gh does.
 
@@ -55,6 +59,8 @@ command):
                                             successful `gh pr merge`
     gh fake fails '<command> <subcommand>'  make every such call fail, e.g.
                                             'issue close'
+    gh fake user-email '<JSON>'             set the public profile email, an
+                                            address or null
 
 Every call's argv is appended to the JSON list in $FAKE_GH_RECORD.
 
@@ -307,8 +313,12 @@ def issue_close(state, positional, flags):
 
 
 def api(state, positional, flags):
-    """The two commit endpoints thirdshift reads CI from, one page, each item
-    of the list `--jq '.<list>[]'` names on its own line."""
+    """The signed-in user, or the two commit endpoints thirdshift reads CI
+    from, one page, each item of the list `--jq '.<list>[]'` names on its own
+    line."""
+    if positional[0] == "user" and not flags:
+        print(json.dumps({"login": "runner", "email": state.get("user_email")}))
+        return
     match = re.fullmatch(
         r"repos/([^/]+/[^/]+)/commits/([0-9a-f]+)/(check-runs|status)(\?.*)?",
         positional[0],
@@ -387,6 +397,8 @@ def fake(state, args):
         state["after_merge"] = args[1]
     elif args[0] == "issue":
         state["issues"][args[1]] = args[2]
+    elif args[0] == "user-email":
+        state["user_email"] = json.loads(args[1])
     elif args[0] == "fails":
         state.setdefault("failing", []).append(args[1])
     elif args[0] == "pr":
diff --git a/tests/setup.rs b/tests/setup.rs
index 4936ef65c..08beb249d 100644
--- a/tests/setup.rs
+++ b/tests/setup.rs
@@ -1,5 +1,6 @@
 //! `thirdshift setup`: Setup writes a complete User config. With no terminal
-//! and no User config, it writes every setting at its default without asking.
+//! and no User config, it writes every setting at its default without asking,
+//! and `email.to` as the GitHub email it suggests, if it finds one.
 
 mod support;
 
@@ -22,6 +23,12 @@ fn user_config(scenario: &Scenario) -> Option<String> {
     fs::read_to_string(scenario.path("home/.thirdshift/config.toml")).ok()
 }
 
+/// The `email.to` the User config sets, if it sets one.
+fn email_to(scenario: &Scenario) -> Option<String> {
+    let config: toml::Table = user_config(scenario)?.parse().unwrap();
+    Some(config["email"].get("to")?.as_str()?.to_string())
+}
+
 /// The lines of `text` that set a key, commented out or not, as
 /// `(section, line)`.
 fn key_lines(text: &str) -> Vec<(String, String)> {
@@ -41,6 +48,7 @@ fn key_lines(text: &str) -> Vec<(String, String)> {
 #[test]
 fn with_no_terminal_and_no_user_config_setup_writes_the_defaults() {
     let scenario = Scenario::new();
+    scenario.git_email_is(None);
 
     let result = scenario.run(&["setup"]);
 
@@ -73,6 +81,7 @@ fn with_no_terminal_and_no_user_config_setup_writes_the_defaults() {
 #[test]
 fn every_key_is_written_with_a_comment_giving_what_it_does_and_its_default() {
     let scenario = Scenario::new();
+    scenario.git_email_is(None);
 
     scenario.run(&["setup"]);
 
@@ -138,7 +147,10 @@ fn a_run_with_the_written_user_config_behaves_as_with_none() {
 #[test]
 fn a_run_with_the_written_user_config_still_needs_an_address_for_email() {
     let scenario = Scenario::new();
+    scenario.git_email_is(Some("123+runner@users.noreply.github.com"));
     assert_eq!(scenario.run(&["setup"]).code, Some(0));
+    assert!(email_to(&scenario).is_none());
+    let setup_calls = scenario.gh_calls().len();
 
     let result = scenario.run_with_env(
         &["--email", &scenario.issue_url(7)],
@@ -152,6 +164,8 @@ fn a_run_with_the_written_user_config_still_needs_an_address_for_email() {
         result.stderr
     );
     assert!(scenario.claude_calls().is_empty(), "the Run started");
+    let run_calls = &scenario.gh_calls()[setup_calls..];
+    assert!(run_calls.is_empty(), "the Run asked GitHub: {run_calls:?}");
 }
 
 #[test]
@@ -213,3 +227,91 @@ fn setup_refuses_a_user_config_a_run_would_refuse_and_leaves_it_alone() {
     );
     assert_eq!(user_config(&scenario).as_deref(), Some(broken));
 }
+
+#[test]
+fn setup_writes_the_public_github_email_as_email_to() {
+    let scenario = Scenario::new();
+    scenario.github_email_is(Some("octo@example.com"));
+
+    let result = scenario.run(&["setup"]);
+
+    assert_eq!(result.code, Some(0), "stderr: {}", result.stderr);
+    assert_eq!(email_to(&scenario).as_deref(), Some("octo@example.com"));
+    let text = user_config(&scenario).unwrap();
+    assert!(!text.contains("# to = "), "{text}");
+    let to = key_lines(&text)
+        .into_iter()
+        .find(|(_, line)| line.starts_with("to = "))
+        .unwrap()
+        .1;
+    assert!(to.contains(" # ") && to.contains("default"), "{to}");
+}
+
+#[test]
+fn with_no_public_github_email_setup_writes_the_git_email() {
+    let scenario = Scenario::new();
+    scenario.github_email_is(None);
+    scenario.git_email_is(Some("me@example.org"));
+
+    assert_eq!(scenario.run(&["setup"]).code, Some(0));
+
+    assert_eq!(email_to(&scenario).as_deref(), Some("me@example.org"));
+}
+
+#[test]
+fn when_gh_api_user_fails_setup_writes_the_git_email() {
+    let scenario = Scenario::new();
+    scenario.github_profile_fails();
+    scenario.git_email_is(Some("me@example.org"));
+
+    let result = scenario.run(&["setup"]);
+
+    assert_eq!(result.code, Some(0), "stderr: {}", result.stderr);
+    assert_eq!(email_to(&scenario).as_deref(), Some("me@example.org"));
+    assert!(
+        scenario
+            .gh_calls()
+            .iter()
+            .any(|call| call[..2] == ["api", "user"]),
+        "{:?}",
+        scenario.gh_calls()
+    );
+}
+
+#[test]
+fn a_noreply_git_email_is_never_written() {
+    let scenario = Scenario::new();
+    scenario.git_email_is(Some("123+octo@users.noreply.github.com"));
+
+    assert_eq!(scenario.run(&["setup"]).code, Some(0));
+
+    let text = user_config(&scenario).unwrap();
+    assert!(!text.contains("noreply"), "{text}");
+    assert!(text.contains("\n# to = "), "{text}");
+}
+
+#[test]
+fn with_neither_email_setup_writes_email_to_commented_out() {
+    let scenario = Scenario::new();
+    scenario.github_profile_fails();
+    scenario.git_email_is(None);
+
+    assert_eq!(scenario.run(&["setup"]).code, Some(0));
+
+    let text = user_config(&scenario).unwrap();
+    assert_eq!(email_to(&scenario), None, "{text}");
+    assert!(text.contains("\n# to = \"you@example.com\""), "{text}");
+}
+
+#[test]
+fn setup_never_replaces_an_existing_email_to() {
+    let scenario = Scenario::new();
+    scenario.github_email_is(Some("octo@example.com"));
+    let mine = "[email]\nto = \"mine@example.net\"\n";
+    scenario.user_config_is(mine);
+
+    let result = scenario.run(&["setup"]);
+
+    assert_eq!(result.code, Some(0), "stderr: {}", result.stderr);
+    assert_eq!(email_to(&scenario).as_deref(), Some("mine@example.net"));
+}
diff --git a/tests/support/mod.rs b/tests/support/mod.rs
index 1fb72c3ec..7521dff50 100644
--- a/tests/support/mod.rs
+++ b/tests/support/mod.rs
@@ -238,6 +238,38 @@ impl Scenario {
         self.write_gh_state(&gh);
     }
 
+    /// Set the public email of the profile `gh api user` answers with: an
+    /// address, or `None` for a private one.
+    pub fn github_email_is(&self, email: Option<&str>) {
+        let mut gh = self.gh_state();
+        gh["user_email"] = json!(email);
+        self.write_gh_state(&gh);
+    }
+
+    /// Make every `gh api user` call fail.
+    pub fn github_profile_fails(&self) {
+        let mut gh = self.gh_state();
+        let failing = gh.as_object_mut().unwrap().entry("failing");
+        failing
+            .or_insert(json!([]))
+            .as_array_mut()
+            .unwrap()
+            .push(json!("api user"));
+        self.write_gh_state(&gh);
+    }
+
+    /// Set the global git `user.email`, or with `None` unset it.
+    pub fn git_email_is(&self, email: Option<&str>) {
+        let change = match email {
+            Some(email) => ["user.email", email],
+            None => ["--unset", "user.email"],
+        };
+        git(
+            &self.path("home"),
+            &[&["config", "--global"][..], &change].concat(),
+        );
+    }
+
     pub fn gh_state(&self) -> Value {
         serde_json::from_str(&fs::read_to_string(self.path("gh-state.json")).unwrap()).unwrap()
     }