Can you send me any links how can I solve it? :/

I have installed WP Mail SMTP and the same thing happend. For now it's possible to use this link in GMAIL (but it also comes with < and >), but ...

Do I have to setup it somehow, or just install?

I'm using only clean WP + WpForo, no more plugins related to mails.

Ah okay. I get this error when I try to register new account. Mailbox does not matter, I have tried 4 different mailboxes. The problem is all e-mails ...

Any tips? :/

Of course it's about Wordpress. Mailbox does not matter here, just check screenshot from GMAIL mailbox. The same thing. It's wordpress adding "<" a...

What do you mean? I'm using newest WP, and I posted screenshot from my mailbox located on different website. 🙂