String matching is inherently fuzzy. I haven't tested it, but I think a dropdown box to select your account would be best. This would also help with other norma

String matching is inherently fuzzy. I haven't tested it, but I think a dropdown box to select your account would be best. This would also help with other normalizations (accents, spaces), and even typos if user enumeration is not a problem. I put abuse detection system in the same category as tests, it gets a free pass on most cleanliness requirements. The typed strings pattern is a great one. In this case you could go as far as having a RegisteredEmail types, and requiring that in your MailerHelper.