What type of retrieval are you using? Is this an IMAP/POP based sync or are you using one of the heftier sync protocols? Does the issue affect all users or only some? To start I'd increase the retrieval logging detail levels for whichever protocol you're using, then test retrieval into a new separate test account so you can isolate it in the logs. It could be a variety of things but those logs should get you going in the right direction :-)

IMAP/POP3

POP3 is enabled as well. All validated.

Hello John,

Please go under: Manage > Troubleshooting > Options > Process Logging. 

Here you will find IMAP Retrieval and POP Retrieval. Please set these to Detailed and review the logs when SmarterMail attempts to retrieve next. Hope that helps!

Thanks, ticket submitted.