SMB solo SysAdmin here. I have a decent amount of experience with Exchange, but need to be sure we have no issues as we get into our busy season of the year (we're a greenhouse). Our sales staff keeps coming to me with stuff like this:
"So-and-so sent this email on Tuesday and we just got it today (Friday)! What's wrong with our email server?!" (email was an @mail.com address, BTW. "Free" ad-driven service, probably garbage and not suited for business)
"This is the second week in a row this person's email didn't come through! Please fix this!!" (email address was @suddenlink.net)
So, more to the point, my questions are:
If the Microsoft Online Connectivity Analyzer (https://testconnectivity.microsoft.com/) says we have no issues with inbound/outbound SMTP, then the problem is either their email server or just human error, right?
Similarly, our transaction time (according to http://mxtoolbox.com/diagnostic.aspx) is about 7.5 seconds, which is maybe not the best, but surely wouldn't cause a 24-48 HOUR delay, right?
Lastly, We also use an Untangle UTM for anti-spam (paid version), BUT I have whitelisted the addresses in question and also didn't find them in the spam quarantine.
Thanks for your help, I appreciate it!