In Odoo 11 C version,

Any replied message for those mails which were sent from Odoo, doesn't seem to come back into Odoo.

For example:

In SaleOrder, via Log note, a mail was sent to UserA's Gmail Account,

Then UserA replied for that mail from his Gmail, However his reply didnt come into Odoo portal.

Infact delivery-failure mail coming for catchall@

Note: Outgoing Mails are working perfectly, just the replied mail doesn't come into Odoo.

Am I missing something