turtleattacks:

 

Technically the emails have been sent successfully but the Google email server delivering the 'email package' is regarded as SPAM, hence it really should be Google that takes responsibility. 

 

Thanks for this guys, because the emails we send are medically sensitive and time critical. We simply can not afford emails being blocked/regarded as SPAM. 

 

I'll make the arrangements of migrating our mail service to Microsoft O365 next week. 

 

Just a word of caution... you might want to check if Microsoft offer a dedicated IP address option for your email sending, otherwise you could potentially have exactly the same issue.

quick check looks as if they do... https://docs.microsoft.com/en-us/dynamics365/marketing/dedicated-vs-shared-ip