I have installed Sitecore 9.1 on my local machine - Windows 10 and trying to run a sample campaign using out of the box EXM using custom smtp (using my gmail server).
The EXM shows a success message but no email actually being sent or received. The EXM.Master.Campaign table shows the "Status" as "Sent" but "FailedRecipients" count of all contacts (4 in my case):
I tried to get into the logs and but could not found any error. Any help is appreciated.
Updated: Updated with another screen shot to give more clarity: