I have an issue that's driving me crazy. Running Ubuntu 12.04 on DigitalOcean, I followed this tutorial to set up Postfix, Dovecot, ViMbAdmin and RoundCube:

https://rtcamp.com/tutorials/mail/server/postfix-dovecot-ubuntu/

Everything has been working fine for almost a week so far until suddenly today my incoming mail started getting stuck in the queue. I can see the emails using postqueue -p but they've just been sitting there for over 5 hours.

I am able to send email to other hosts just fine, but I can't receive emails I send to myself either.

In my mail.err log I keep seeing lots of this:

Apr 8 16:10:30 marcusforsberg master[14769]: fatal: master_spawn: exec /usr/lib/postfix/f: Permission denied

But nothing else in the error log, just that line over and over.

The mail.log file keeps giving me this:

Apr 8 15:48:07 marcusforsberg master[5841]: fatal: master_spawn: exec > /usr/lib/postfix/f: Permission denied

Apr 8 15:48:08 marcusforsberg postfix/master[5758]: warning: process /usr/lib/postfix/f > pid 5841 exit status 1

Apr 8 15:48:08 marcusforsberg postfix/master[5758]: warning: /usr/lib/postfix/f: bad > command startup -- throttling

And for each email:

Apr 8 15:46:05 marcusforsberg postfix/qmgr[5770]: 7D40416365E: from=, size=5691, nrcpt=1 (queue active)

Apr 8 15:51:40 marcusforsberg postfix/qmgr[5931]: 7D40416365E: skipped, still being delivered

Running postqueue -f has no effect, nor has resetting the Postfix config (dpkg-reconfigure postfix), restarting Postfix or rebooting the server (this has worked before when e-mail got stuck).

I've spent the better part of the day researching this but I haven't found much useful. The only change done before this started malfunctioning was that I rebuilt my DigitalOcean droplet from a snapshot. Before this, everything was working just fine. I had seen the "Permission denied" errors regularly as well but I was still able to receive email.

Here is my main.cf for Postfix: http://pastebin.com/hrxhkWZ7

And my master.cf: http://pastebin.com/mV9GcUNi

If anyone has any suggestions or links to solutions I have missed, please do let me know. Or if I should share any other configuration files or logs.

Thanks in advance for any help!

(This is a repost of my question on DO, where I haven't had much luck. I hope that is allowed and that this is even a good place for this question... Please let me know otherwise!)