Can't Register with Email Address - Email Format

Hi

A user on our website was trying to register an account with their email address in the format: firstname.lastname@hotmail.com

The website will not allow them to create an account and checkout as the email address appears to be invalid?
How can I change this to allow email addresses in the format: firstname.lastname@hotmail.com

Please advise asap.
kind regards
FG

bump

What version of opencart?
Is there anything that has been changed or is this unmodified version?

Mike

I'm having this issue too.

Opencart 2.2 but it's done it throughout the versions.

It happens randomly, gmail bigpond.com etc.

Any help with this?