当$ header达到一定长度时，php mail（）不发送邮件

My PHP mail() always stops sending email when the From header reaches a certain length. I’m using Cyrillic symbols in the From header, so I have to encode it in windows-1251 (that’s the only encoding that seems to work in all HTML mail clients I need to support).

So, my code:

$to = 'myemail@test.com';
$subject = 'Cyrillic subject goes here';
$message = $letterbody; //letterbody gets form data and packs it into nice table
$headers = "MIME-Version: 1.0
";
$headers .= "Content-Transfer-Encoding: 8bit
"; 
//takes Lastname of the person registering, encodes it so all the clients can read, takes its email address
$headers .= "From: =?windows-1251?B?".base64_encode($lastname)."?= <$email>
"; 
$headers .= "Content-type: text/html; charset=\"windows-1251\"
";
mail($to,"=?windows-1251?B?".base64_encode($subject)."?=",$message,$headers);

So, for example, I set the $email variable to test@test.com and set $lastname to "tttt". The email sends and $headers looks like this (taken from a var_dump() right before sending):

MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
From: =?windows-1251?B?dHR0dHQ=?=
Content-type: text/html; charset="windows-1251"

If I add one more "t" with the same email address

$email = test@test.com;
$lastname = "tttttt"

the mail does not send and the $headers look like this:

MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
From: =?windows-1251?B?dHR0dHR0?=
Content-type: text/html; charset="windows-1251"

I have no idea what else I can do. With no encoding of the $lastname it seems to be working fine, but then it’s unreadable on some email clients, such as Postfix on Ubuntu 13.

Maybe I need to set some $headers limit in Postfix?