We have had a few issues with phpmail() not being delivered to Hotmail. However, this is quite strange and seems to be a per software issue.
We use WHMCS & Kayako like most other companies, but when we try sending out email from WHMCS using the phpmail() option, emails are not received by clients that use Hotmail. However, when we change to the SMTP option, they do receive the emails. Kayako is always set to use phpmail() of some sort and all clients using Hotmail are receiving our emails.
We have also had a few clients come to us saying that phpmail() of some sort is no longer sending emails to Hotmail accounts. For instance, one of the cases was IPB forum board was no longer sending email to Hotmail accounts using phpmail().
I am just enquiring to see if any has an insight or fix for this or if it is Hotmail actually causing the problems by refusing phpmail() from certain applications/software.
When using the php mail() function, the email appears to come from teh user nobody in most people's case. Hotmail is much more likely to reject this email because so much spam comes through looking the same from forums and the like.