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.
As mentioned by @douggro this isn't really doable. But as a workaround, you can setup a dummy POP3 account that will never receive any mail and then uncheck "Include when automatically checking for new messages".
So the question becomes, how to get a dummy POP3 account. At first I tried a Gmail account with POP3 enabled. But OS X tries to be smart and does a bunch of things with Gmail accounts that cause it to present a login webpage all the time.
However, I found this awesome service called MailTrap.io which gives you one free "testing" inbox.
- So go to https://mailtrap.io/ and click signup in the top right.
- You can use your Google Account or Github Account to signup quickly.
- Then you will be taken to a testing inbox where you will see a POP3 username and password.
- Enter all those credentials into Mail.app (be sure to check "Allow insecure authentication") and, importantly, for the outgoing mail server, use your custom SMTP (I like Mailgun and Mandrill for my custom domain).
All this is free. You should see an empty mailbox in Mail but just ignore that and send and receive mail as normal.