Mail Subject cause SPAM

[rhodarose]

I have code for mail subject:

$Mail->Subject = 'Preview/' . $this->csvUploadPaymentDetails[0]['csvfilename'].'/'.date('d-m-Y').'/'.$this->csvUploadPaymentDetails[0]['week_num']; 

The problem is the mail was become SPAM, I got this message
Mail delivery failed: returning message to sender. How can I prevent my email become not SPAM?

When my subject is only this: $Mail->Subject = 'Preview'; it works, but I need my subject is

 $Mail->Subject = 'Preview/' . $this->csvUploadPaymentDetails[0]['csvfilename'].'/'.date('d-m-Y').'/'.$this->csvUploadPaymentDetails[0]['week_num']; 

, because I need to have filename,date, and weekno in my subject.

It's my first time to encounter this error.

Thank you..any help is highly appreciated.

[traq]

are you sure it's being filtered as spam, and not failing for some other reason? for example, what does your variable csvUploadPaymentDetails[0]['csvfilename'] contain? RFC2822 limits the number of characters you can put in an email header (e.g., Subject line) to 998 (and only 78 per line). You might find this useful.

If your email is being ID'd as spam, then you need to change the content of your Subject line. it looks like you're putting a filename in your subject now; that seems like it might be suspicious in the eyes of a spam filter. In any case, there are no hard rules about avoiding spam: email clients all do this differently, and are constantly updating their criteria.