Mail.app Conversation/Threading issues like RES: RES: RES:

Solution 1:

The threading does happen based on subject. Re: is ignored; so Re: Re: Re: foo is the same as foo, and the same as Re: Re: foo. That's why it works.

What is RES:? Is it Re: in a different language? That's why it's breaking - because RES is not being ignored and therefore looks like a different subject.

The person you're conversing with needs to use Re:, not RES:. RES: may be inserted automatically by their email client; in which case you may need to find a different way to group the emails, perhaps by sender.

There are tools that can help, though. With MailTags (http://www.indev.ca/MailTags.html) you can group/organize your email much differently or simply use the subject renaming feature. With MailActOn (http://www.indev.ca/MailActOn.html) you can match a rule that moves the email to a specific folder ignoring the "RES" part, etc. There are many options.

No, I am not affiliated with Indev, I just use and love their products. :-) Best of luck.

Solution 2:

"RES: " isn't the correct E-mail subject abbreviation in Portuguese.

The correct one is: "RE: " (= Reposta), as documented on Wikipedia: list of Email subject abbreviations → Portuguese.

Fix the E-mail client which is providing you with this wrong field. No E-mail client configured to work with a Portuguese environment will understand it.