Some emails sent via mail() on my server are not reaching their destinations. I've checked the mail logs and I have no log entries since Aug 5th. I'm not sure where to begin looking into what might be the problem. I have confirmed that some mails are being sent/received.
Verify your mail log
using your preferable editor open
Verify if sendmail is up and running
Stop and restart sendmail to make sure you have no error within it and to flush your db
NOTE: This command may differ from OS to OS;
Verifying Address Resolution and Aliasing
For hosts that resolve to IPC mailers, MX hosts are not reported when using verify mode, because MX records are not collected until delivery is actually attempted.
If the address is not being resolved as you expect, you may have to modify one or more of the following:
More detailed information about how the configuration file is rewriting the recipient addresses is provided by address test mode:
Contacting the sendmail Daemon to Verify Connectivity
It is possible to talk to the sendmail daemon and other SMTP servers directly with the following command:
This can be used to determine whether an SMTP server is running on host. If not, your connection attempt will return "Connection refused."
Once you establish a connection to the sendmail daemon, you can use the SMTP VRFY command to determine whether the server can route to a particular address. For example,
Not all SMTP servers support the VRFY and EXPN commands.
You might want to use something like tshark to confirm that data is leaving your box to be delivered. If you have one available, try using a smarthost, preferably the one for your ISP, and also, take a look at SRV records