We currently have Exchange 2013 sitting on a Server 2012 VM at a site of ours. The mail is currently running through a smart host for Spam Filtering. There are multiple distribution groups under multiple domains configured and set as 'reply to' so the users can change their From address. Whats happening it they have people theyre sending to report that mail is not getting through to them and vice versa. This isnt constant, and happens randomly throughout the week. They arent receiving any NDRs and it doesnt appear that things are getting stuck in the Queue or in the receiving parties spam filter. Also at times it seems that mailflow is extremely slow, sometimes taking up to 10-15 minutes for mail to go through. After a few days, they will actually lose connection to Exchange all together which requires a server reboot to bring the connection back up. If I run Test-MailFlow, I receive *FAILURE*. Basically im looking for a good place to start troubleshooting. I feel that theres issues on both the server side, as well as software.