I experienced this periodically on my gmail and always assumed that it was just a typo on the part of the sender, adding a period where there shouldn't be one.

I experienced this periodically on my gmail and always assumed that it was just a typo on the part of the sender, adding a period where there shouldn't be one. But there were cases that kind of defied plausibility, like when a recruiter (sharing my name but not my gmail address) sent out a mass cold email and I got the angry replies. I never figured out how that one happened, maybe they misconfigured their mailer software's replyto? I never once considered that a gmail bug or intentional design decision could be at work there. TIL that they decided to cut down on the confusion by normalizing addresses.