POP3 Mail retrieved from O365 is changing alias address into primary address

Hello

We have in our O365 environment some functional mailboxes where a primary address is set to ex. 

test@test.be

The alias is being set to :

test.alias@test.be

Whenever a mail is sent in O365 to the alias, the to header is kept intact ( to: test.alias@test.be )

When that mail is retrieved via poP3 / 995 : it seems the to field is change to the primary address : test@test.be

Has anyone seen this behaviour?