Attachment is going to Gmail but not other mailboxes - php

Question

These are the headers which I am using to send email with an attachment, however the attachment only gets through to Gmail. For all other mailboxes I tried, only the message content arrives, without the attachment.
# Define the main headers
$header = "From:$from_email1\r\n";
$header .= "MIME-Version: 1.0\r\n";
$header .= "Content-Type: multipart/mixed; ";
$header .= "boundary=$num\r\n";
$header .= "--$num\r\n";
# Define the message section
$header .= "Content-Type: text/html\r\n";
$header .= "Content-Transfer-Encoding:8bit\r\n\n";
$header .= "$message1\r\n";
$header .= "--$num\r\n";
# Define the attachment section
$header .= "Content-Type: multipart/mixed; ";
$header .= "name=\"test.txt\"\r\n";
$header .= "Content-Transfer-Encoding:base64\r\n";
$header .= "Content-Disposition:attachment; ";
$header .= "filename=\"$cv_view12\"\r\n\n";
$header .= "$encoded_content\r\n";
$header .= "--$num--";
# Send email now
$retval = mail ( $to, $subject1, $message1, $header );

Answer 1

What's the size of the attachment?
Gmail has a 25mb attachment limit, which is a lot larger than many email providers.
Now, I'd expect you'd get a bounce-back message telling you that the attachment is too big if this is the case, but if the email address you're using for "From" is not valid, this wouldn't bounce back to anywhere you could see.
I'd start by setting a valid "From" address and see if you get any messages back as to why.
I also highly recommend Swift Mailer:
http://swiftmailer.org/
Which takes a lot of the complexities out of sending mail, and may automatically fix a small typo in manually creating a mail message. There is also a lot of advanced functionality built-in which makes life much easier.