PHP mail undelivered

In several of my pages hosted in DH, I have a small piece of PHP code to manage mail delivered from a form. Mails from this pages were received fine up to May, but from there and uptoday it doesn´t work anymore.
I tried entering my page from the web and sending me a test contact-mail and I get messages as if the mail has been correctly delivered, but in reallity it never arrived to my mail recipient. If I send a mail from my Outlook to the same mailbox it flows without problem so the maibox is functioning OK.
Any suggestions about this issue?

I remain waiting for your answer, tks in advance

Most likely it’s the FROM header causing the problem. A long time ago you could spoof the FROM header and use almost any email address as the FROM. Due to spam dreamhost changed policy and required the FROM header to be from your own domain.

There are numerous threads in this forum on the topic since, but the announcement was originally made here: in April of 2012.

Tks LakeRat for your answer. Althought I read the original info (2012) but my mail worked fine up to June 2013.
I´m going to try your suggestion. Thanks a lot.

If you look for other threads in the forum, it’s apparent that there may have been a loophole or glitch somewhere in the implementation. Over time various posters have said that this was working beyond the cutoff and suddenly stopped. After altering the FROM to an address associated with their domain the issue goes away.