First off let me give some background. I am running a single exchange server (exchange 5.5 sp3) on NT 4 sp6a. I believe the problem started when I changed my DNS, it was ?mail.domain.com? and my exchange server name is ?something_mail?. The DNS change I made was that the reverse DNS reflect my mail server?s name ?something_mail.domain.com? instead of ?mail.domain.com?. I did this because email were getting rejected from a company?s domain, the reason being, when their server checked my reverse DNS it didn?t reflect the correct server name in the header so the messages were being rejected. For the first week everything seemed to be working fine, so I thought. Then, I started getting complaints that a select few people from certain domains couldn?t email us. It looks like 2 or 3 domains receive kickback when trying to email us; I receive all other incoming emails. Here is the header/error info I have received: -----The following addresses had permanent fatal errors---- user@xxxxxxxxxx ----Transcript of session follows---- 550 5.1.2 user@xxxxxxxxxx ? host unknown (name server: something_mail.domain.com.: host not found) this is what my DNS table looks like: domain.com. in mx 10 something_mail something_mail in A 0.0.0.0 (exchange ip address) domain.com in A 0.0.0.1 (website ip address) www in A 0.0.0.1 (website ip address) Reverse record 0.0.0.0 (exchange ip address) in PTR something_mail.domain.com From the research I have done it seems the ?_? in my exchange server name is causing problems. (I think) My question is can I change my exchange name in my outgoing email headers with out reinstalling exchange. Any suggestions or work around would be greatly appreciated. Please give step-by-step instructions or tell me where to get the needed info. Thanks in advance Jim