A customer raised an interesting observation about Gmail addresses. See: https://support.google.com/mail/answer/7436150?hl=en
From this link:
For e.g., if your email is firstname.lastname@example.org, you own all period versions of your address:
How does Campaign handle period versions of email addresses? Is there any out-of-the-box (OOTB) schema or workflow that helps distinguish accounts from period or non-period versions? Is it up to the customer to setup some sort of Regular Expression (RegEx) to capture the right account (If so, has anybody set something like this before)?
Adobe Campaign Standard (ACS) does not do special cases for email addresses internally. Periods are considered as normal characters and are never ignored, as this can be clearly a violation of the Request for Comments (RFC) standard.
As periods don’t matter in Gmail addresses, hence the same rule is followed in Adobe Campaign as well.