Why do some emails get logged in mail manager and some don't?

Question

Hi, 
 We have a UTM320 v9 and our own mail server. 
 When users call and tell me they think an email to them got stuck in quarantine or bounced back, my first step is to check the SMTP Log in the Mail Manager to see if it even made it here. But I sometimes find emails in the SMTP Log under Logging & Reporting->View Log Files->SMTP Proxy that do not appear at all in the mail manager. 
 Why would this be? Why would there even be a log in the mail manager if it doesn't log everything? 
 Thanks, 
 Jeff

Scott_Klassen · Accepted Answer

This appears to be the greylisting process at work, which will be reflected in the raw log, but not in the Mail Manager Log. Do you understand what greylisting is and how it works? Emails from an unknown address will be temporarily rejected by the UTM. A properly configured and valid sending MTA (email server) will then retry after a certain interval (set on the sending server) and the UTM will accept the retry, adding the address to its' greylisting good list. I'm thinking that you may not be leaving enough time for the sending email server to retry (generally can be anywhere from seconds to 15 minutes). 
 If you find there are some valid senders whose MTAs never retry, you just need to create an exception rule to skip greylisting for those sender addresses/domains.

BAlfson · Answer

With an Exception. 
 Cheers - Bob