Good morning! I'm sending emails daily to a specific contact, and everything works fine. However, once per week, my Exchange Server is not able to deliver the email, sending me: Your message did not reach some or all of the intended recipients. Subject: XxXxXxXxXxX Sent: 2/17/2011 3:32 PM The following recipient(s) cannot be reached: x.XxXxXxX@XxXxXxX.com on 2/17/2011 3:32 PM There was a SMTP communication problem with the recipient's email server. Please contact your system administrator. <XxXxXxXxXxXx.XxXxXxXxXxXxX.XxXxXxXxX #5.5.0 smtp;550 x.XxXxXxX@XxXxXxX.com... No such user> The problem is that everything had worked fine, using the same contact. To solve this, I need to edit the contact (just open it and rewrite the email - the same email) and resend. And then, it'll work for 4 or 5 days, until I need to do that again. The email is ALWAYS typed ok, always. It seems, to me, like the Exchange is not recognizing the string as an email recipient... but why? Thanks for helping me. Take care <!-- [if gte mso 10]> <mce:style>

That isn't an Exchange error. Therefore it is outside of your control. I suspect that the recipient may have multiple MX records, or the MX record host is supported by multiple hosts and one of those doesn't recognise the user. Nothing you can do about it, the recipient needs to query with whoever operates their mail server. Re-entering the address doesn't really do much other than mean Exchange has to do a fresh DNS lookup on the MX records and may well deliver to another host. Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

Thanks for your answer Sembee. Actually, re-entering the address worked fine, if I edit the contact first. It seems to me that, editing the contact will erase it from the Outlook cache list, and then, it'll work. It's so stranger. And the recipient domain is a domain used a lot in my company (we are always sending email to them). Unfortunately, one recipient causes this problem once a week. First, I thought it was an Outlook problem. So I've tested in 2003, 2007 and 2010 versions, and the problem happened in the three versions. Is that a way to check if the recipient has multiple MX records? I'm using Exchange Server 2003. Thanks

Hi Marcelo, We could use nslookup to check it or use http://www.mxtoolbox.com/ to check it. Regards! Gavin TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

Just another detail... the undeliverable email wast sent to three recipients, all with the same domain. But just one recipient caused the undeliverable message. And the problem is always with this recipient. Thanks for all help.

Thanks Gavin-Zhang, actually the domain has 3 MX records. But I don't think this is the problem, because everyday we send a lot of emails to this domain, and the problem happens with just one recipient. Any ideas? Thanks a lot.

Hi Marcelo, Per your description, in my opinion, the issue maybe caused by the recipient's email address had been changed or removed in the recipient domain. I would suggest that you could use other email box (such as hotmail) to send a email to the recipient, and we could check the email address whether is exists or not. Regards! Gavin TechNet Subscriber Support in forum If you have any feedback on our support, please contact tngfb@microsoft.com Please remember to click Mark as Answer on the post that helps you, and to click Unmark as Answer if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.