E-mails sent by me go to SPAM folder or are not received at all

Hello!

The e-mails I send are not being received or being sent directly to the Spam folder in other domains.

I checked all the information related to how avoid that situation, but nothing works (like not using Caps Lock in the Subject, for instance).

What can I do to avoid this problem? Is this a shared problem or just related to e-mail?

My domain is outlook.pt

Thank you very much in advance.