MailFromSmtp

IMPORTANT NOTE: MailFromSMTP is now deprecated and will no longer be maintained. Here are some highlights as to why:

• In macOS 10.12 (Sierra), Mail.app restructured the way that outgoing accounts are assigned to the compose windows. This means that selecting the SMTP server dynamically has now become much more challenging.
• There is a more maintainable solution to this problem if you are running your own mailserver, which is to use SMTP forwarding when emails are sent from certain addresses (see below).
• If you did happen to be using this plugin on macOS 10.10 or 10.11, then this should continue to work fine.

Postfix-based solution

If you are running postfix, then you can set up the sender_dependent_default_transport_maps option to define relays that will forward mail to remote servers based on the From header in your email. First, create a directory /etc/postfix/header-relays to keep configuration files related to this in (and also keep everything neat), then set up a hash /etc/postfix/header-relays/sender_transport_map which defines the email addresses that should be filtered:

email1@gmail.com          smtp1:[smtp.gmail.com]
email2@otherserver.com    smtp2:[smtp.otherserver.com]

Then, run postmap on this file to generate a .db file, and enable this in your main.cf configuration with:

sender_dependent_default_transport_maps = hash:/etc/postfix/header-relays/sender_transport_map

Each SMTP relay requires a configuration with your authentication details. For example, my configuration file for smtp1 lives in /etc/postfix/header-relays/smtp1.relay and looks like:

[smtp.gmail.com] email1@gmail.com:password

Again, you should run postmap on these files to generate the .db. Finally, you need to update your master.cf to define each transport smtp? that's defined in the sender transport map. For example, mine look like:

smtp1      unix  -       -       y       -       3       smtp
    -o smtp_use_tls=yes
    -o smtp_sasl_auth_enable=yes
    -o smtp_sasl_security_options=noanonymous
    -o smtp_sasl_password_maps=hash:/etc/postfix/header-relays/smtp1.relay

You can then restart postfix, and send an email with the appropriate From: header set using the addresses dropdown in Mail.app. If you monitor your logs, you should hopefully see that these email is forwarded to the appropriate SMTP relay.

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What is (was) this?

In OS X 10.10 (Yosemite), Apple removed a useful feature from their Mail.app client: the ability to change which SMTP server you use from within the message editor. After some communication with Apple via their bug tracker, they claim that such a feature is not useful/required and therefore will not be re-added in future versions of Mail.app.

Since Mail.app supports 'bundles', which can extend the functionality of the client (albeit in an unsupported manner), this project reimplements this functionality, using the SMTP servers that you have set up and an email address that is associated with each one. It is therefore 'better' in the sense that you don't have to select which email server you'd like to use -- MailFromSMTP will figure that out for itself.

Why would I want this?

If you are not sure this is useful for you and your setup, this is mine: I have a single IMAP account which aggregates all of my email using fetchmail. I therefore want the ability to send email from multiple addresses, depending on context.

Mail.app allows you to define multiple outgoing identities, by defining them as a comma separated list in the Email Address field in the account information. This causes a From: drop-down list to appear in the message composition editor.

MailFromSMTP tries to identify an SMTP server to send outgoing email by comparing it against the From: address you selected, and will automagically send via this server if it finds a match. If not, then it will use your default SMTP server.

Bonus feature -- automatic signature selection

Because I use this for my personal email, this bundle includes another, rather unrelated feature. When you change the From: field, it will try to match a signature and automatically put this into the mail body. For now, to use this feature you need to modify the source, so I leave this as an exercise for the interested user.

Requirements

• OS X 10.10
• Xcode 6.1

Caveats

1. Since this uses Mail's private API, it will almost certainly break at some point in the future. However, I do plan on updating as new OS versions come out.
2. You need to have multiple email aliases set in your email account. To do this, define them as a comma separated list in the Email Address field in the account information. See e.g. http://bit.ly/1hfR1DQ for instructions.
3. Each SMTP account you have configured in your mail client should have a CanonicalEmailAddress set in ~/Library/Mail/V2/MailData/Accounts.plist. To do this, open up this file in e.g. TextEdit, find the DeliveryAccounts key, and for each email account, make sure you have an entry such as

   <key>CanonicalEmailAddress</key>
   <string>my@email.address</string>

4. I will probably not maintain this beyond my own personal use, although pull requests are highly encouraged.

Installing

1. Clone the repository
2. Open the Xcode project
3. Compile
4. Locate MailFromSmtp.mailbundle by right clicking on the MailFromSmtp.mailbundle product and select Show in Finder.
5. Create the directory ~/Library/Mail/Bundles if it doesn't exist.
6. Copy MailFromSmtp.mailbundle into ~/Library/Mail/Bundles.
7. Enable Mail bundles by issuing the command defaults write com.apple.mail EnableBundles 1 at a terminal.
8. (Re)start Mail.

License

This is distributed under the GPLv3 license, with the exception of Swizzler.m and Swizzler.h which are shamelessly copied from stl's MailBundle-Template project.