Links not clickable in emails sent by sendmail - but only on some Blackberrys

Bit of a long shot, but I’ve run out of places to ask. So, can anyone help with this one?

We are using PHP sendmail to send HTML emails to a list of customers, inviting them to click on a link to complete a survey. Everything works fine and has done for years, except that recently some people reading the email on a Blackberry report that the link is not clickable - the link is there, but the email client on the Blackberry is not recognizing it as a link and so clicking on it does nothing. They report that it is only our emails that have this problem - other emails with links in work perfectly. After trawling through many fora, I’m none the wiser, except that someone reported a similar problem with emails sent from the Simple Machines Forum software, which also uses PHP’s sendmail function - it was something to do with setting the right MIME type. But our emails are pure HTML, so there is no “multi-part” requirement.

Can anyone offer any suggestions?

Are you sending the html mails yourself (using mail()) or are you using a library such as PHPMailer, or even better, Swift Mailer?

You should try using Swift, as it’ll generally help solve a bunch of problems like this. We use to have all sorts of problems with HTML mails in different clients, but since we started using Swift (and PHPMailer) they’re pretty much solved.

We’re using PHPMailer V5.1. We’ve never had a problem before and must have sent out thousands of emails.

Mostly link problems occure on mobile devices when the quotes are not given properly. Do you have

 <a href="">click here</a> 

instead of the wrong

<a href=''>click here</a>