Hi Joao,
Thank you for posting, May i know when is the last time you able to send and receive mail?
I am here to help. For the meantime please try this steps see if this will help:
Turn off or disable Antivirus temporary check if you will receive mail or send mail by sending a test mail to your mail account.
If you are using Outlook online try to clear cache and cookies your Web browser and try again if you can send test mail to your outlook account.
looking forward to helping you out. If you need more help please let me know. If the answer is helpful, please click "Accept Answer".
Best regards,
Jansher