# Unique Identifier & Duplicates - how does this work?

**URL:** <https://forum.mautic.org/t/unique-identifier-duplicates-how-does-this-work/22037>\
**Category:** Product Support\
**Created:** [December 16, 2021, 9:23am UTC](https://forum.mautic.org/t/unique-identifier-duplicates-how-does-this-work/22037 "2021-12-16T09:23:46Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![mikew](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.mautic.org/mikew/32/5156_2.png) [@mikew](https://forum.mautic.org/u/mikew)\
**Post date:** [December 16, 2021, 9:23am UTC](https://forum.mautic.org/t/unique-identifier-duplicates-how-does-this-work/22037/1 "2021-12-16T09:23:46Z")

</div>

**Your software**  
My Mautic version is: 4.0.2  
My PHP version is: 7.4  
My Database type and version is: mariadb 10.4

**Your problem**  
My problem is:

We have an instance setup where we have both emails and mobiles set up as unique identifiers, and I am seeing multiple contacts with the same email and mobile.

I am not sure exactly how this is meant to work - if anyone can shed some light on the matter