The first clue would be the emails that aren't being sent (or received). Is there any pattern there, namely a certain domain? If so there's a chance that your server is blacklisted by that email provider. This is very common. If it's a dedicated server, you can look at your server's mail log. Generally you'll see error codes of 550. Drupal won't know about this, and report the email as sent without any problem (your server had no problem, but the receiving server did. By that time sendmail has already sent a passed response back to PHP).
Like I said, this is very common. The only real fix is to find the problem email servers in your mail log then check their sites for how to get removed from the blacklist. AOL is one in particular that can be a pain, and they commonly blacklist IP's they don't know. Whenever I set up a new dedicated server for a client, I always account for this when giving an estimate. It's just that common!
The other option is to use a separate email service for your domain, like Google Apps. Then you can use the SMTP module to send all emails and not have to worry about all this stuff.
Jamie Holly http://hollyit.net
On 1/8/2014 6:46 PM, Marty Landman wrote:
I have run into an issue on Ubercart conditional actions where some emails simply don't get sent. There is no error message and I'm at a loss. When I change to another email I get them, so am unsure how to start looking for a clue here. Nothing on the dblog, the order goes through properly according to the UC admin screen, and the server error log has nothing to add either.
Marty