smtp ACCOUNT

You’re posting in the macOS 13 Ventura forum, but reference “phone”, so I’m unsure which you’re using. Both?

That error isn’t usually related to sending a mail message, it’s related to configuring or re-configuring the SMTP server settings. Or maybe possibly due to a corruption, if (for instance) iCloud Keychain has gotten itself tangled. iCloud Keychain getting tangled has happened here very rarely and only on older macOS versions, and that only usually around very flaky network connections.

What to do?

Remove and re-add the mail accounts, and try again.

Or clean up the SMTP accounts that might be present. Settings > Mail > Accounts > pick an account > Account> (outgoing mail server) SMTP > review the list of SMTP servers there for correctness, as compared with your mail providers’ expectations.

rail buff wrote:

Get this error when trying to send email from long-time account

"An account of type “SMTP” already exists. Only a single “SMTP” account is allowed to be saved."

Both accounts have been on phone for years.

Did you verify with your email provider there is not a server issue on their side(?) this would be out of your control

try again in a few hour/days and compare your results