As I outlined in my comment; humans attempting validation of email addresses like this using patterns and words and domains that they know about is doing things incorrectly. Guide them as bluntly or as gently as you feel is necessary and or proper to educate them on what modern email addresses can look like.
You maybe able to inform someone who might be expecting your email address to be at a common domain name that they should not make that assumption and that they should be double checking them regardless of what provider(s) they assume the person they are helping is using anyways.
Someone asking you to repeat your email address again is a GOOD THING! It means they’re paying attention to inputting it into their system(s) correctly; It is mildy annoying when people assume that I use a common provider anyways, as they might inadvertently attempt to incorrectly “upgrade/update” my email address to the domain they use or know.
An example I’ve experienced: I owned an original @googlemail.com GMail account. Until they mothballed the @googlemail.com domain I used it in that format. Inattentive people would attempt to substitute @gmail.com. Another issue would be that My actual Username on said GMail account is a direct mispelling with one letter transposed into an incorrect position. This Misspelling is intentional, and it used to work to my advantage to dodge spambots using dictionaries to guess email IDs. Therefore for a short time people would attempt to “correct” it and I would always prefix my email address explaining they need to input it exactly as I spell it out.
I suppose when dealing with E-Mails it is simply critical to make sure they repeat it back to you before submitting it. This is simply to avoid your E-Mails being mis-delivered anyways; which in some cases can be a Massive Headache when it does happen.