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Setting up an email provider - Google Mail/Apps, Outlook, etc - seems straightforward for a single domain. In the case of multiple subdomains, can different email providers be used on a per-subdomain basis?

Some examples to show what I'm thinking:

joe.example.com - joe@example.com - Google Apps
jane.example.com - jane@example.com - Outlook
mary.example.com - mary@example.com - Google Mail
junior.example.com - junior@example.com - some other provider

The key being that each subdomain has a matching email address, though not necessarily all from the same email provider.

Can each subdomain be configured independently for email provision, or must it be a homogeneous setup?

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    Interesting question, but there is a problem with your examples. The subdomains from the left column are missing from the center column. The top line should read joe.example.com - joe@joe.example.com - Google Apps for example. – Tom Brossman Feb 8 '14 at 18:02
  • @TomBrossman I figured that an email account could be set with the domain portion matching the actual web domain. But the way I wrote the examples is actually what I am asking about. Having a shared main domain, with individual subdomains, where the subs are the users of the email address main domain. – Grant Palin Feb 9 '14 at 0:46
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Each sub-domain may have a specific email service provider designated to it using DNS MX records, however the domain portion of the email address is what determines the MX records that are read and therefore the mail server which receives the inbound emails.

For the solution you have requested where different mail service providers are used concurrently for a single domain a more complicated setup is required, and to be honest its not a great solution. This is a problem I come across all the time, particularly with small businesses and charities who may have a large number of users who are happy with a standard web-mail interface and SMTP/IMAP to send/receive emails from their desktops and mobile devices, but perhaps only a handful of users that need a full exchange setup with shared folders, shared calendars, task management, global contact lists and Active-Sync push mail to their mobile devices etc. Unfortunately the mail server configuration cannot be configured per email address and must always be a per-domain configuration.

I have included 3 options here for how you could proceed, mainly to ensure you're aware of them all and have considered them, but in terms of answering your question where you have specified you would like to concurrently use a selection of email providers and from a single domain name, and do not wish to consolidate to a single email provider for all your email users, your only realistic option for moving forward is likely to be Option C below.

Option A: Email Provider Consolidation

You all choose to standardise on the email platform you will use on that domain name - for example all of you use Google Apps or all of you use Office 365 or all of you use another provider. This is the only solution which will enable you to both send and receive email with the branding of the primary parent domain (@example.com).

Option B: Domain Name Separation (using different gTLD's)

If there are only a couple of mail providers to use concurrently then sometimes companies have managed this split by using an @example.com domain for one provider and an @example.net or @example.org for the other provider. By using a different domain name for each email provider there is no longer a routing problem, and to avoid any lost messages from confusion or guessed email addresses, you could setup email aliases/forwarders at each domain to ensure all messages reach their intended mailbox users. For example:

Email Provider 1 (example.com): junior@example.com --> junior@example.net
Email Provider 2 (example.net): joe@example.net --> joe@example.com

Option C: Mail Forwarding at Parent Domain

  • You configure the different MX records for each of the sub-domains as preferred by each mailbox user, and create mailboxes at each respective email service provider. To give an example, for joe@example.com you would configure the following MX records:

joe.example.com IN MX preference:10 exchange:aspmx.l.google.com joe.example.com IN MX preference:20 exchange:alt1.aspmx.l.google.com joe.example.com IN MX preference:30 exchange:alt2.aspmx.l.google.com joe.example.com IN MX preference:40 exchange:aspmx2.googlemail.com joe.example.com IN MX preference:50 exchange:aspmx3.googlemail.com

  • And then at the parent domain, point the MX and A records to mail servers for which there is a control panel you can access to configure email forwarding (substituting your server IP addresses for my made up ones):

example.com IN MX preference:10 exchange:mx1.example.com
example.com IN MX preference:20 exchange:mx2.example.com
mx1.example.com IN A 111.222.333.444
mx2.example.com IN A 111.222.333.444

  • From there you can create an email alias/forwarder to redirect:

joe@example.com --> joe@joe.example.com
mary@example.com --> mary@mary.example.com
etc...

  • This will automatically route Joe's inbound email to Google Apps for him, however when he responds to his messages they will appear to come from and then setup a Mail forwarder/alias to redirect inbound emails received at joe@example.com to joe@joe.example.com.

  • To help with managing this, if you're not keen on seeing repetition in your email addresses perhaps you would choose your sub-domain names based on the email provider, for example: joe@googleapps.example.com, jane@outlook.example.com or junior@office365.example.com, or if you like shorter versions how about joe@ga.example.com, jane@ol.example.com and junior@o365.example.com.

    If users are sending/receiving their email from Microsoft Outlook desktop software then you could configure the software to use the Google Apps IMAP server for receiving messages but to use the SMTP server of your parent domain for sending messages and then they would appear to be sent by joe@example.com.

    The same method can be used from mobile devices, but as far as I'm aware it is not possible if you are logging into the Google Apps web-based system or outlook.com or Office 365.

  • Appreciate the detailed response. Fortunately after some investigation of preferences and needs, I was able to consolidate on a single provider - Outlook.com - using a custom domain. With the use of aliases and forwarding, I have a setup with multiple discrete users seemingly using the same primary domain. – Grant Palin Mar 27 '14 at 1:52
  • I'd really like it if it were possible to have all the different providers lined up as MX records in order, and if the first one doesn't have the mailbox it could be configured to say "I don't know that one but try the next MX record" rather than just "I don't know that one so it doesn't exist". There are some other email standards for ways of doing things on a mailbox basis but in general the majority of email server software hasn't adopted these methods. – richhallstoke Sep 14 '17 at 9:41

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