I don't know why I am having this issue... I have moved from a shared host to a VPS solution and have had to hit the ground running due to having no previous VPS experience (maybe that answers my question...).\n\nOne of the domains I have moved over uses Google Apps for handling its email service, which has worked fine in the past. I moved the domain over to the VPS, adjusted the MX records for the domain's DNS on the VPN, and all was good. Emails were being sent to Google as expected. But then I added a few subdomains through DirectAdmin control panel (similar to cPanel) and ever since I have been getting a delivery status notification when I try to email my Google Apps email account.\n\nA couple of things worth a mention:\n1) I can still refresh the inbox via IMAP in Thunderbird just fine for the Google Apps email account, so that tells me the DNS should be correctly configured, at least partially, or it wouldn't find it at all, right? At least the MX record should be...\n2) These test emails that bounce back immediately are being sent from a Gmail account to a Google Apps email account. It doesn't matter whether I use Gmail's own interface or Thunderbird, so I don't think it's an SMTP server misconfig on my part.\n3) I have not had time or opportunity to test if sending an email to mika [ə] salakka dot com would work from a non-Google-operated address yet.\n\nThis is an example of the delivery status notification I get back from Google (I have manually edited the email addresses within to be harder for email harvesters to read):\n\n[QUOTE]Delivery to the following recipient failed permanently:\n\n mika [a] salakka.com\n\nTechnical details of permanent failure: \nGoogle tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 authentication required (state 14).\n\n-\-\-\-\- Original message -\-\-\-\-\n\nReceived: by 10.204.45.152 with SMTP id e24mr494472bkf.47.1303437602930;\n Thu, 21 Apr 2011 19:00:02 -0700 (PDT)\nReturn-Path: <salakka [a] gmail.com>\nReceived: from [22.214.171.124] (ZYYYKMMCDXVIII.gprs.sl-laajakaista.fi [126.96.36.199])\n by mx.google.com with ESMTPS id 16sm1419360bkm.6.2011.04.21.18.59.59\n (version=SSLv3 cipher=OTHER);\n Thu, 21 Apr 2011 19:00:01 -0700 (PDT)\nMessage-ID: <4DB0E11D.50001 [ə] gmail.com>\nDate: Fri, 22 Apr 2011 04:59:57 +0300\nFrom: Mika Salakka <salakka [ə] gmail.com>\nUser-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:188.8.131.52) Gecko/20110223 Thunderbird/3.1.8\nMIME-Version: 1.0\nTo: mika [a] salakka.com\nSubject: gyyyttttttttg\nContent-Type: text/plain; charset=ISO-8859-1; format=flowed\nContent-Transfer-Encoding: 7bit\n\nthyhjyhgtgt t jhjh hhhhh[/QUOTE]\n\nI'm not wild about posting the DNS record from the VPS here out in the open; I can PM it if someone thinks it can tell them something.\n\nI am not entirely convinced this isn't a problem at Google's end; it is just that the timing coincides with my creation of those subdomains.