diff --git a/docs/config.md b/docs/config.md
index 071218d7..7083b656 100644
--- a/docs/config.md
+++ b/docs/config.md
@@ -980,7 +980,7 @@ variable before running the `ntfy` command (e.g. `export NTFY_LISTEN_HTTP=:80`).
 | `smtp-sender-from`                         | `NTFY_SMTP_SENDER_FROM`                         | *e-mail address*                                    | -                 | SMTP sender e-mail address; only used if e-mail sending is enabled                                                                                                                                                              |
 | `smtp-server-listen`                       | `NTFY_SMTP_SERVER_LISTEN`                       | `[ip]:port`                                         | -                 | Defines the IP address and port the SMTP server will listen on, e.g. `:25` or `1.2.3.4:25`                                                                                                                                      |
 | `smtp-server-domain`                       | `NTFY_SMTP_SERVER_DOMAIN`                       | *domain name*                                       | -                 | SMTP server e-mail domain, e.g. `ntfy.sh`                                                                                                                                                                                       |
-| `smtp-server-addr-prefix`                  | `NTFY_SMTP_SERVER_ADDR_PREFIX`                  | `[ip]:port`                                         | -                 | Optional prefix for the e-mail addresses to prevent spam, e.g. `ntfy-`                                                                                                                                                          |
+| `smtp-server-addr-prefix`                  | `NTFY_SMTP_SERVER_ADDR_PREFIX`                  | *string*                                            | -                 | Optional prefix for the e-mail addresses to prevent spam, e.g. `ntfy-`                                                                                                                                                          |
 | `keepalive-interval`                       | `NTFY_KEEPALIVE_INTERVAL`                       | *duration*                                          | 45s               | Interval in which keepalive messages are sent to the client. This is to prevent intermediaries closing the connection for inactivity. Note that the Android app has a hardcoded timeout at 77s, so it should be less than that. |
 | `manager-interval`                         | `$NTFY_MANAGER_INTERVAL`                        | *duration*                                          | 1m                | Interval in which the manager prunes old messages, deletes topics and prints the stats.                                                                                                                                         |
 | `global-topic-limit`                       | `NTFY_GLOBAL_TOPIC_LIMIT`                       | *number*                                            | 15,000            | Rate limiting: Total number of topics before the server rejects new topics.                                                                                                                                                     |