Horde Webmail problem

[David Enfinger]

This is strange. my customers are having a hard time with https://webmail.thierdomain.com some of my customers can access thier webmail and some cant. Some of my customers can access the webmail sometimes and sometimes not. All of my sites are set up the same way in the dns. Also the default site which is mine I have no problem accessing email at any time. Is any one having problem and what should I check next. I am running a windows 2003 server with plesk 6.5.2. I am also behind a firewall. I have had customers shut off thier firewall and they are still getting errors.

Thank you in advance