Mail processing and delivery seems very slow and there are a lot of emails in the Mail Queue.
First make sure you have the latest Libra Esva version and that there is no underlying problem, next:
1. Make sure that there are no actual problems with MailScanner by tailing /var/log/maillog to check for any errors, looping, etc. Certain types of problems can sometimes lead to MailScanner causing high server loads. tail -f /var/log/maillog
2. Check to see how many mails are currently waiting to be processed by MailScanner, with: postqueue -p.
If the queue is quite large, you may want to consider temporarily disabling scanning in order to get the pending mail processed, before trying to resolve any possible problems.
To do this, go to menù System->Networking and System Services->Core Services and stop MailScanning.
When the queue is back down to 0 or close to it, you can Enable Scan Messages again.
3. Check DNS lookup speed. Make sure you are using your local resolver, i.e. on the server if you’re running a caching nameserver. Check to make sure that is resolving quickly by doing a dig on a random domain name.
4. Make sure the SpamAssassin Bayes database is not too large, and delete it if it is too large. Check in Tools > SpamAssassin Bayes Database Info for the number of tokens (less than 500.000 is best), last journal sync and last expiry. Expiry should be getting done on a daily basis. If the bayes database is very large, it would be best to delete it and start over: rm -Rvf /var/spool/mqueue/.spamassassin
5. You can test spamassassin to see if it is hanging on anything in particular, under menu Tools -> SpamAssassin Lint Test6. General server checks. Make sure that your disks have plenty of free space and there are no actual hypervisor problems.
IMPORTANT: most of the time the delivery delay is due to a slow hypervisor. Check twice virtual disk latency and virtual machine performances.