Hi almeida_pedro,
Thank you for posting in Apple Support Communities.
We'll be happy to see how we can help out with the Mail app on your Mac/book Pro.
From what you are describing, it sounds like rebuilding the mailbox would be what we recommend. It's a lot more simple than it sounds, and it helps with unusual Mail app issues that sometimes appear.
Rebuild mailboxes in Mail on Mac
You may need to rebuild a mailbox to update the list of messages it contains. For example, if messages appear to be missing or garbled, or if you can’t find all relevant messages when you search using the Entire Message search option.
1. In the Mail app
on your Mac, select a mailbox in the sidebar.
2. Choose Mailbox > Rebuild.
When you rebuild mailboxes for IMAP or Exchange accounts, messages and attachments stored on your Mac are discarded and then downloaded again from the mail server to your Mac. Your mailbox appears empty until the download is complete.
You can find all this information in the article Rebuild mailboxes in Mail on Mac.
Reach back out if you still need help.
Take care!