MacOS – Disable outgoing mail for an account

There is a preference you can set so that composing a new message defaults to a specific mailbox rather than the currently selected mailbox.

Replies go from the account to which the message was addressed. I'm not sure how it breaks a tie if both of your addresses are included or copied, but you can always override the "from" account by clicking on your name / email under the subject field.

In the message composition window, there's a pulldown above the message body, on the right, to select which email address you're sending from. The default for this depends on which mailbox you have selected in the main Messages window. It sounds like you're doing this.

If you're sure the above is being done for sure, then it's possible some gmail filters or tagging is getting in the way and making it look as though the reply lands in the inbox for one when really it's in another.

I would check the webmail and see if the issue is also seen there. If it is, then you're likely not sending from the right account, even if you think you are.

Typically, if you had many people from your Contacts you would simply create a group by following:

1. Open Contacts.app and select "File" -> "New Group"
2. Enter the name of the group you are creating.
   • This is what you will type into mail, and will effectively be the name of your "distribution list".
3. Go back to "All Contacts" and drag the contacts in that you would like to be in your group.
4. Now, when you want to sent to that group, just type in the group's name and Mail.app will automatically populate the sending information.

However, for your situation, that won't work very well as you need to create a distribution list for many people who aren't in your Address book (per your edit). With a tip borrowed from iOS, and a hack, you should be set.

1. Your list of email addresses must be comma-delimited. If it is separated by line breaks, then this likely won't work. So first we need them comma delimited.
2. Now we will create a contact, and name it "2013 4Q Students" or something.
3. Next, we will put our comma-delimited list of email addresses into one email field.
   • I assume there is an arbitrary limit on how many email addresses you can put into one field, but I don't know from experience what that might be.
4. Type the new "contact" name into a Mail.app compose "To" field. It will come up with the standard blue bubble and all those email addresses will be packed inside.
5. Now we proceed with a small hack: click the down-arrow next to the contact name in the blue bubble.
6. Click "Edit Contact".
7. Remove the contact name ("2013 4Q Students") from the beginning and the "<".
8. Type Command + right arrow to reach end of email address line, and remove the ">".

Just a little cumbersome, but this should work for you.