In Apple Mail it is possible to send an email message from a different email address than the one associated with the email account you are using to send/receive through.
What do I mean by this? Check out the following examples. For the solution, look further down.
Some examples of the problem
One example: I use email forwarding addresses a lot. This is an alias address that forwards to a real email address/account.
For instance, if I am providing an email address to a web site I don’t necessarily trust with my address (will they sell it to a spam list?) I will provide them with a unique alias or forwarding address. I set up this unique address on my mail server as a forwarder. For example, firstname.lastname@example.org forwards to email@example.com. In this example firstname.lastname@example.org is my real email address, and sitename@ is the name of the site I am giving an email address to, such as during an account registration process. This way if I ever receive spam to this forwarding address I will know exactly where the address was leaked from.
But here is the issue: What if I later need to send someone (the site owner, for instance) an email from email@example.com? With Apple Mail there is no obvious way to do this.
Another example: I use a Gmail account to consolidate emails from a number of other accounts I have. Gmail checks these accounts for me. Gmail even lets me send out messages as though the message originates from one of these accounts. It works well. Gmail has great spam filters so I find it useful to run all my email accounts through Gmail.
Apple Mail has fairly good IMAP support and allows me to access my Gmail account over IMAP. This works well enough and this is how I access my Gmail account. But what happens when I receive a message that was sent to one of the accounts Gmail is checking for me? If I hit reply in Apple Mail, there is no way to send the reply FROM the account that originally received the message.
I recently had this problem with Paypal. I’d sent them a message from my Paypal account using the Email Us form on their web site. Their reply came in by email to a Gmail account that consolidates emails for me. I replied in Apple Mail but then got told by Paypal that they could not correspond with me because the message I sent them did not come from an address not associated with my Paypal account. I had to log into Gmail in order to reply because there was no obvious way to do it in Apple Mail.
It turns out that Apple Mail has an easy way to resolve this problem, but it is not at all obvious and not explained anywhere in Mail Help (not as far as I could see).
Go to Preferences > Accounts. Looking at the “Account Information” section there is the field “Email Address:“. Normally you just have the email address of the relevant account stored here. But it turns out you can add as many other email addresses to this field as you like, in effect making a comma separated list of email addresses. Just put in here any other email addresses you may need to send from via this primary “master” account (the account being used to consolidate email addresses from forwarders and from Gmail, etc.).
Here is how it looks: (firstname.lastname@example.org is the primary account address)
Now when you reply to a message or write a new message you will be able to select any of the addresses you’ve listed here as the From address. Under the Subject field you should see a From field. Here is an example. You can see the dummy email addresses I put into the example above:
If you do not see the From field, click the little options icon as shown in the following image (it has three lines and a downward triangle on it (I have circled it in red in the above image):
Select “Customize” and you’ll see something like this:
Put a tick next to “From:” as shown in the above example.
Now when you send messages you can select which email address to send them from. That’s it.
This solution came from a tip shared by user “Mal” on MacRumors here: http://bit.ly/medx9z
GMAIL users – Important
If you are using a Gmail account to consolidate your emails from multiple accounts into one gmail account you’ll need to ensure a few settings are correct in your gmail account settings.
In Account Settings (on your gmail account) go to the “Accounts & Import” tab. Look for the “Send mail as” section. (Refer to the image below for an example).
Here you need to add the email addresses you want to send mail from (via Apple Mail). Once you have completed setting up each “send as” account everything should work fine.
Having to select correct address when replying to mail?
Some readers have pointed out in the comments below that each time they reply to a message they have to select the correct From address because it is not selected automatically. I have not had this issue, and as I am now on OS X 10.7.x (LION) I can not test what the situation was/is on Snow Leopard. Using Mail 5.2 I find that the correct From address is selected automatically when I reply to an email (assuming the message was sent to email@example.com, for example, and I have firstname.lastname@example.org set up in the comma separated list of address as per the instructions laid out in this article).