Those companies can take care of Grandma.
If this really is just a protocol, and not a marketing name, then the main thing it needs to do is be inoffensive and distinguishable. Honestly, I would be much more comfortable starting a company around a protocol named something super-dumb like MURP or another non-descript acronym.
There are probably names that are just as bad for other reasons, but one of the top goals of naming something like this should be avoiding getting targeted as something intended for illegal use.
Nobody's grandmother uses or avoids Gmail because of any connotations of "Simple Mail Transport Protocol", because they never hear about it. Only the most crazy religious people (or the least imaginative trolls) ever get upset by "mailer daemon"
This, if successful, will be marketed as "Gmail's new secure mail feature" or "SparrowSecure Mail.app" or "$ISP's privacy-enhanced mail option", not as "dark mail, the replacement for your smtp imap and pop3 service".