Canonicalize email addresses and flag duplicates by provider rules
Emails to normalize
How normalization works
Gmail / Googlemail
Gmail ignores dots in the local part and treats anything after + as a tag. j.doe+sales@googlemail.com and jdoe@gmail.com resolve to the same mailbox.
Outlook / Live / Hotmail
Outlook accepts +tag aliases that route to the base address. Dots are not ignored — only +tag suffixes are stripped.
Why normalize?
Useful for deduplicating mailing lists, abuse detection, and account-uniqueness checks where users may try to register variants of the same address.
Caveats
Other providers may also support tagging, but their rules vary. When in doubt, leave the address untouched and rely on the trim/lowercase pass alone.