Update February 2016: Mandrill has announced changes that if I understand them correctly would mean for my sending volume I’d go from paying $65 in the past two years to $30/month in the future. Needless to say, I’ll be moving away from them a.s.a.p. and do not recommend them anymore to anyone! Of course I am not the only one who is not happy about that. While I have yet to properly evaluate alternatives, Mailgun looks promising. I’ll update my plugins when I’ve moved to another service.
If you have a server that needs to send mail, I highly recommend using a specialized service such as SendGrid or my personal favorite Mandrill (up to 12k sends per month are free). While integrating Mandrill in certain web software is easy (like their wpMandrill plugin for WordPress), vBulletin is a bit more tricky.
While it is easy to configure vBulletin to send mail through Mandrill (just create an API key and configure mail in the vBulletin settings) a problem is that the vBulletin Contact Us form uses the user’s email address in the “From:” field and that pollutes your Mandrill account very quickly.
As solution I’ve written a little plugin that rewrites the “From:” field into a “Reply-To:” field and then adds your webmaster email address as “From:” field, which solves this issue.
Now on to one of the neat things you can do with Mandrill: automated handling of bounced mail. Mandrill supports webhooks where you can have certain events be reported to automatically, such as “hard-bounce” or “reject” email events. Such a webhook can then take action on this information.
I’ve written a Mandrill webhook for vBulletin that will automatically move a user to the “Users Awaiting Email Confirmation” usergroup if such an event occurs, so that no more mail is sent to them (until they update and reconfirm their email address), which will improve your email delivery score.
The plugin and webhook plus further info can be found here: https://bitbucket.org/ghdpro/vbulletin-mandrill
Tip: for greater security, limit your Mandrill API key access (in Mandrill settings) to your server’s IP address and for vBulletin (or any service that only uses SMTP access) you only need to allow the “send-raw” API call, nothing else.