Just fyi,
Email issues are a hard road to track.
Could be blacklists, could be host server issues.
Could be individual client security software.
Could be connectivity issues.
I have had all of those issues in the past.
Best thing to do is test with a constant variable.
Then deal with different browsers, isp providers and mail clients.
Also don't forget that some hosts that brag unlimited hosting also throttle how many emails per hour or minute you are allowed to send.
They don't tell you that until you call and complain.
They may get delayed or deleted.
It is a pain in the ***.
