MyBB Community Forums

My forum mail goes automatically to spam.
This issue born when I installed, years ago, a plugin that sends automatic emails to members who don't connect for months.
How can I bypass this issue
I already have disabled the plugin I'm worried some people selected as spam my mails...

Your IP must have been blacklisted. It is a common issue with people who send spam emails to members. Try a different hosting provider.

If I send emails through SMTP I can bypass the issue without change hosting?

Email providers like Gmail and Outlook have a very advanced system to detect spam email. I am not sure how effective your method will be. Personally, I will use a third party forum email service to send forum emails.