My mother was also a one-l MAILER but I have come across many variations in the twenty-seven years I have been researching the name. MAILLER is the most common - just have a look in the IGI - and seems to have become a fairly common surname today (not that any Mailers are common!). I don't know whether this has arisen out of errors in transcription by various recorders, but I have come across it in the UK, Australia, Canada and the US. One Auchterarder family I have done some research into lived in both Stirling and Aberdeen and the parish registers there spelt the name as MAILEAR. I've learned to keep my eyes open when researching MAILER, you never know how it's going to be spelt, and it's a pain wading through MAHLERs! I would love to hear something about your MAILER research.