Validating email address form
According to this RFC, "Neither part of the address may end with a dot".
Even if it wasn't, though, this would be something to raise to PHP rather than Drupal...
We are sorry but we had to abort your free email validation because of the heavy load our systems are experiencing. Also please note that our paid email validation service does not have this kind of limitation.
With Verifalia you can easily upload and validate your email address lists and receive detailed reports.
For example, if you ask for email addresses, you can make sure that people can only submit properly formatted email addresses.A character set indicates that just one of the given character(s) should occur in the current position.For the most part, any characters are valid within brackets, including characters mentioned previously in expressions: [xa,Gg.]A character set range signifies a search for a character within the given range of characters. Ranges can be combined into a single range: [a-z A-Z0-9].Ranges can also be combined with character sets (mentioned previously): [a-z A-Z,&*].NOTE: When trying to search for actual instances of any character that has a specific meaning in regular expressions, like ^ and $, you need to "escape" the character in your search query by placing a backslash in front of it.