UBB.threads PHP Forum Software Community Forums UBB.threads Version 7/8 Support New User Not Getting "Password" E-Mail

I have a user who states that he has registered with our Forums, but has not received the Forum generated e-mail with his password. I went into the Admin section and requested that his password be e-mailed again.

I received this message as a result (I put the "xxxxxx" string in):

I've received a number of these messages over the last several months, with the common thread being "rediffmail.com". I just blew this off at first as some sort of spam nonsense, but now a legitimage user is e-mailing me from this domain.

I've read other posts here, that state the ISP on the other end could have some filters in place. What can I advise the user to look for? What advice should I request that he pass on to his ISP? (I just can't imaging what in the password e-mails would get trapped by a filter ...)

Could be a couple of things. The "invalid HELO hostanme" looks like whatever hostname your mailserver is initiating the request as is blacklisted or blocked on their end. They would probably need to contact their provide with your mailserver hostname and find out if it's blocked and why.

Additionally, there are a ton of utilities online to check if your server ip, or the requesting server ip, are blacklisted; one of which is:
http://www.mxtoolbox.com/blacklists.aspx