Use only SMTP server without a mailbox In Mail.app I have several mail addresses and incoming mail to some addresses is already being forwarded to my primary mail address. I don't want to have an inbox for these secondary emails (I've got them on my primary anyway) but I want to be able to send from those addresses. I've tried adding my secondary account as usual, and then disabling it. But then I can't see that address' SMTP server to send from when sending. If I enable it, I can see it, but its mailbox automatically comes back. How can I have no mailbox for a mail account, but still be able to select its SMTP server to send mail from that address?
In short, you can't accomplish what you're trying to do. In order to send/reply from a given address, you have to have that account set up and active in Mail.

Without the account being active, the address you wish to use is not available. And setting up an SMTP server entry for the other account(s) will not bypass the primary issue since you would only be using any alternate SMTP server as a relay for the account you're using to send the email - it will not rewrite the sending account address. For example, I have email forwarded from a generic "info@" account to a personal account on the same domain, but I can't reply with or send from the "info@" account address since I don't have that account set up in Mail.