This article explains how to remove an outgoing mail server in the macOS Mail app. This information applies to the Mail app in macOS Catalina (10.15) through Mac OS X Mavericks (10.9), except where otherwise noted.
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Apple's macOS Mail lets you set up multiple outgoing email servers. This flexibility can be useful at times, but it's useful to know how to delete SMTP server settings if you no longer need them. For example, maybe the server settings are no longer relevant to your email accounts, or maybe they're old and broken.
Regardless of the reason, you can delete SMTP settings in macOS Mail using the following steps.
Open the Mail app and select Preferences under the Mail menu.
