2 mails collected by email account linked to same issue for default email_account "Support"

Hi community !

I’m using erpnext 14, and I have tried with erpnext 15.

I’m trying to automise auto assignment for issues, created automatically by email account.

I have setup 2 email accounts for my tests.
The email account “Support”, setup automatically when I have setup erpnext, I have just change connexion parameters
A second email account “Custom”, with same parameters.

When the email account collect 2 mails with same from, and same subject, he linked automatically this 2 mails on the same communication and same issue.

With the same mails, the email account “Custom” create 2 distincts communications and tickets.

I have no rule on email, and I have verified my parameters.

the account behavior “Custom” is what I expect, but I just want to understand this difference.