The local part of the email address may use any of these ASCII characters:
uppercase and lowercase Latin letters A to Z and a to z;
digits 0 to 9;
special characters !#$%&'*+-/=?^_`{|}~;
dot ., provided that it is not the first or last character unless quoted, and provided also that it does not appear consecutively unless quoted (e.g. John..Doe@example.com is not allowed but "John..Doe"@example.com is allowed);
space and "(),:;<>@[] characters are allowed with restrictions (they are only allowed inside a quoted string, as described in the paragraph below, and in addition, a backslash or double-quote must be preceded by a backslash);
comments are allowed with parentheses at either end of the local part; e.g. john.smith(comment)@example.com and (comment)john.smith@example.com are both equivalent to john.smith@example.com.
As you can see from link to the actual code above, posty is currently supporting a very strict subset of this. At the very least it should allow underscores, as they are actually used quite frequently in the real world.
https://github.com/posty/posty_api/blob/master/app/models/virtual_user.rb#L11
From wikipedia:
As you can see from link to the actual code above, posty is currently supporting a very strict subset of this. At the very least it should allow underscores, as they are actually used quite frequently in the real world.