I tested form validators for email field and inputted long email:
$email = 'dfgjfdjglkdfjglkjdfgldfjglkdfjgkldfjlkgjdlkfjglkdfjkgdklfjgldkfjgldlfjgkldfjglkdfjglkdfklgjlkdfjkgkdfjlkgfjldkgkldjfgkljdfkgjlkdfgljdlf@mail.com';
On the local machine function filter_var return string with email:
$email = 'dfgjfdjglkdfjglkjdfgldfjglkdfjgkldfjlkgjdlkfjglkdfjkgdklfjgldkfjgldlfjgkldfjglkdfjglkdfklgjlkdfjkgkdfjlkgfjldkgkldjfgkljdfkgjlkdfgljdlf@mail.com';
die(var_dump(filter_var($email, FILTER_VALIDATE_EMAIL)));
But on the remote server this code returns FALSE.
PHP version on local machine - 5.3.2-1ubuntu4.22
On the remote machine - 5.3.28
Has filter_var function been changed between this version of PHP? Why I receive different values with the same code?
FILTER_VALIDATE_EMAIL has been updated a couple of times since 5.3.2 (you really should update your version BTW). The most notable update was this bug-fix causing a seg-fault when the input/address-to-validate was too long.
Along side this fix (which is logged twice), Rasmus Lerdof on FILTER_VALIDATE_EMAIL returning false positives. Though, AFAIKT, this is not likely to be the cause of your woes.
A couple of other changes include bugs involving special chars like ?, >1 and =.
Anyway, to see all the changes since PHP5.3.2, just check the changelog on their website...
Again: update your local version, it's getting rather dated. Given that you're running ubuntu:
$ sudo apt-get install php5-dev
//optionally
$ sudo apt-get install php5-dev --install-suggests
If you're running mint:
$ sudo apt-get install php5-dev --install-recommends --install suggests
on both distro's, preferably run sudo apt-get update first, of course...
On the PHP's changelog you can see at least two issues (search for FILTER_VALIDATE_EMAIL ) between the versions you mentioned. That could be a starting point to do more searches.
Then what about updating your local PHP version? The one you're using is pretty old...