This is just a brain-dump of everything I’ve learned while stumbling my way through setting up sSMTP with Rackspace email. For the record, I created a single email account on Rackspace and set up sSMTP on my server to authenticate with the credentials for this account.
From line override – @mydomain
When I enabled FromLineOverride, my emails stopped sending. I thought it was spam filters gobbling them up, but it turned out that Rackspace was refusing to send. Looking in the mail log (/var/log/mail.log), I saw this over and over:
RCPT TO:(550 5.1.0 : Sender address rejected: User unknown in relay recipient table)
I fought with this for several hours until the Rackspace help chat technician was able to guide me to a solution. Apparently, if you’re sending emails with a From address from your domain then the From address has to match up to either a real Rackspace email account, or it has to match one of your aliases. Forget about sending from no-reply@mydomain.com unless that’s a real box.
From line override – @mydomain – with catch-all set
Creating a catch-all email seems to change this behavior. Once your catch-all is set, you can send from whatever address you want on your domain. I guess it makes sense, as now any address is a valid return address on your domain.
From line override – @otherdomain
Strangely enough, if you use a From address with a different domain, it all works fine. So, you can pretend all day long to send emails from other domains and Rackspace doesn’t care. But, send an email from a pretend address on your own domain and you’re screwed. Weird.
cron jobs and From line
You have very little control over the From line created by your cron jobs. AFAIK, they’ll always use only the username of the user executing the job. If the output is emailed out then sSMTP will append your domain to this username. Rackspace will reject the email if there’s no account or alias with that name. This means you may need to set up an alias for deploy or whatever user you use for executing your app’s cron jobs, assuming you want to receive the emailed output.
ssmtp.conf is case sensitive
Maybe I’m wrong here, but I swear that ssmtp.conf is case sensitive for YES/NO, even though I’ve seen them used interchangeably in different tutorials. In my case, FromLineOverride only made a difference when I used “no” and not “NO”. Every other YES/NO option seemed to ignore the case. Maybe I’m just crazy.
SPF record
Don’t forget to set up your SPF record! Assuming you’re just going to send email through Rackspace, the following record should work:
v=spf1 include:emailsrvr.com -all
Note: That’s a hard-fail, since I’m a hardass 
DKIM
Nope, not as far as I know. How hard would it be for providers to add this service? Maybe impossible if it would involve them signing emails with your key or something like that.
Well, that’s it. If I’m wrong, or there’s anything I should add, please let me know in the comments.
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