I have performed a new installation of SBS 2011 std for a client. They were using SBS 2003 & I chose to perform a new installation as opposed to a migration, so that no issues would be transferred. I exported the .pst files from SBS2003 & imported then back into the SBS2011 server. The internal domain name & server name were changed. Certain users are not able to send mail to other internal users when using "reply to all". They receive the following error " The e-mail address you entered couldn't be found. Please check the recipient's e-mail address and try to resend the message. If the problem continues, please contact your helpdesk." If they send a message directly (create a new message) it gets delivered. I have cleared the .nk2 cache on the clients, who are using Outlook 2010 or 2007 but the error remains. Here is the diagnostic info. Generating server: SRV01.domain.local IMCEAEX-_O=domain_OU=FIRST+20ADMINISTRATIVE+20GROUP_CN=RECIPIENTS_CN=user1@domain.local #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## IMCEAEX-_O=domain_OU=FIRST+20ADMINISTRATIVE+20GROUP_CN=RECIPIENTS_CN=user2@domain.local #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## IMCEAEX-_O=domain_OU=FIRST+20ADMINISTRATIVE+20GROUP_CN=RECIPIENTS_CN=user3@domain.local #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## Original message headers: Received: from SRV01.domain.local ([fe80::f1c8:ee6a:3401:ea96]) by SRV01.domain.local ([fe80::f1c8:ee6a:3401:ea96%10]) with mapi id 14.01.0218.012; Wed, 16 May 2012 09:12:58 +0930 Content-Type: application/ms-tnef; name="winmail.dat" Content-Transfer-Encoding: binary From: user 1 <user1@domain.com.au> To: Paul Cooke <pcooke@bibendum-wine.co.uk>, 'user 1' <IMCEAEX-_O=domain_OU=FIRST+20ADMINISTRATIVE+20GROUP_CN=RECIPIENTS_CN=user1@domain.local> CC: user 2 <IMCEAEX-_O=domain_OU=FIRST+20ADMINISTRATIVE+20GROUP_CN=RECIPIENTS_CN=user2@domain.local>, user3 Stoodley <IMCEAEX-_O=domain_OU=FIRST+20ADMINISTRATIVE+20GROUP_CN=RECIPIENTS_CN=user3@domain.local>, Alissia Durbridge <adurbridge@bibendum-wine.co.uk> Subject: RE: Company posters Thread-Topic: Company posters Thread-Index: AQHNKDpmBMlhv1q0Sg6Eane/UDWGjpa2LXLggAAAO+CAAABiAIAMHocwgAB+z4CACMS3YA== Date: Wed, 16 May 2012 09:12:58 +0930 Message-ID: <7A497133E2993A448CA183E5281CCB04053DC69D@SRV01.domain.local> References: <9C7D228B812CB14BAD8EB55D9CFA54A00F893703@BWl-RPR-MB02.bwl.local> <EDBBC5D85A00FE4A8A6FD11A57D342790156EE29@server.domain.local> <9C7D228B812CB14BAD8EB55D9CFA54A00F893723@BWl-RPR-MB02.bwl.local> <EDBBC5D85A00FE4A8A6FD11A57D34279015D2709@server.domain.local> <9C7D228B812CB14BAD8EB55D9CFA54A00F8A0986@BWl-RPR-MB02.bwl.local> In-Reply-To: <9C7D228B812CB14BAD8EB55D9CFA54A00F8A0986@BWl-RPR-MB02.bwl.local> Accept-Language: en-AU, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: <7A497133E2993A448CA183E5281CCB04053DC69D@SRV01.domain.local> MIME-Version: 1.0 X-Originating-IP: [10.0.0.33] X-TM-AS-Product-Ver: SMEX-10.1.0.2244-6.800.1017-18906.007 X-TM-AS-Result: No--49.396300-5.000000-31 X-TM-AS-User-Approved-Sender: No X-TM-AS-User-Blocked-Sender: No Regards, Scott