XF 1.5 email issues: Gmail works but others (Yahoo.com, AOL) do not

[SnoSheriff]

email issues:

• works when email is sent to Gmail addy (email land in recipient's email Inbox)
• does not work when email is sent to others like Yahoo.com or AOL.com (email never arrives in recipient's email Inbox or SPAM box)

This happens in all use cases such as: Register New User, Forgot Password, Forum Post Notification, DM Notification... I'm not sure when this issue started but it became a problem once I enabled the 2FA on my website. Please help.

 

[SnoSheriff]

in my Email Options I have the following. Is this correct?

 

[Opus X]

i was told using smtp is more reliable delivery.
something about having to have the server set up right to get good mail deliver uisng PHP.

 

[frm]

Are your DKIM/SPF DNS records set?

 

[SnoSheriff]

It seems to be working now. I checked with the hosting company and apparently the RDNS needed to be set and propagated.

If I were to use SMTP method, what info goes in the Host? Do I need user name and password (if so what goes there)? What do I select for Encryption? How come this method is not recommended and what will be different from the email recipients perspective? Thank you.