My Emails Sent Through PHP Shows As Tags Only For A Few Recipients (sending A Few Hundred)

Im sending out an order conformation for recipients via the simple mail function built into PHP, and this works fine. It's a 'nice' email set up in tables and a few styles with the

Solution 1:

Yes. There are really email clients which do not allow HTML emails. I guess older Outlooks are one of these, too, but not sure.

So, anyway, it is not your fault, it is the user's. See Source 1 and Source 2.

And you can never be sure what does the user's mail program accept. Only plaintext is surely accepted. Quoting Source 2:

"The best you can do is anticipate how each of the major clients will break your design, and then try to control how it breaks, so that it’s still readable by most of your recipients."

It can be solved only with multipart messages, but then some people will get plaintext. See Source 3 for some details on the issue and Source 4 for solutions.

Some documents on this: Source 1, Source 2, Source 3, Source 4

Solution 2:

I've been using Zend_Mail recently (from ZF), which has the option to set a plain text message, and then a HTML message which overrides it where HTML is available. I'm unsure of how this is implemented in the message (headers/etc.) but this could be an answer to your problems.