OMR Info - With more than a few users, use a local/workgroup SMTP server to push the email to OMR

This technote explains the benefits of a local/workgroup server to queue email

At an office or installation, you must configure that location's email clients or network to use OMR. There are two different configuration approaches, with each having benefits and drawbacks.

If you have more than a few users sending mail then there are strong reasons to use a local/workgroup SMTP gateway (does not need to be something complex such as Exchange - we have found that 'Argosoft' mailserver works great for workgroups). The email clients would send mail to the SMTP gateway on the LAN, and the email gateway would send the mail onto TZO's OMR server. The local SMTP server will provide a smoother experience.

For brevity, 'Outlook' is used to both refer to Microsoft Outlook or any other email client.

Benefits of a local/workgroup SMTP gateway

1. General - In the event of any problems, an SMTP gateway will have the intelligence to retry email (if the problem is in fact recoverable - SMTP gateways can determine which errors are temporary and which are fatal).
2. Internet - If your Internet connection becomes degraded, your users can continue to work and respond to email while the SMTP gateway attempts to deliver (or retry) in the background. Outlook and other email clients lack this capability and will present the user with an error message.
3. Quotas - if your installation exceeds your hourly or monthly quota, OMR will return a temporary error (a "421" SMTP code). An SMTP gateway will understand this AS temporary and keep retrying, while Outlook will give the user an error message.
4. Quotas - OMR will accept up to 5 SMTP connections per OMR account. With the sixth connection, OMR will return a temporary error (a "421"). An SMTP gateway will understand this AS temporary and keep retrying, while Outlook will give the user an error message.
5. Connection limits - If the OMR server approaches peak load due to unexpected email volume, the server will continue to respond but it may "defer" some connections with a "421" SMTP code, which is part of the SMTP standard. This code asks the sender to try again in a few minutes. Outlook does not know what to do with this message and will display it. A SMTP gateway will note this, and retry (usually every minute or so).
6. Spam/Virus - If your site becomes infected with email malware or a virus, with a workgroup SMTP server you can limit the damage and also recover more quickly. TZO will notify you and suspend the OMR account temporarily if we see malware or spam reaching the OMR server. We will have no way of identifying 'which' PC on your LAN caused it - but your SMTP gateway's logs can.
7. SMTP gateways pose no additional security liability if you take care to make the gateway unreachable from the Internet. In other words, if you use an SMTP gateway ONLY for a local queue to send onto OMR, then you need not (and should not) expose any additional ports to the Internet. Outbound email gateways should only be reachable from within the LAN space.
8. Timeouts - We have seen cases where the mailserver responds with "OK" 'too quickly' for Outlook (or Outlook not capturing the server response properly). In reality the server confirmation code WAS sent (so the email was accepted), but because Outlook did not see this it will continue to wait, eventually giving the user a timeout message. The user will of course send the email again, possibly causing two messages to arrive at the recipient.
9. Unknown error messages - Another example of Outlook showing the wrong error message to the end user (possibly caused by a local email anti-virus program, which acts as an email proxy for the mail client): http://www.exim.org/exim-html-4.30/doc/html/FAQ_0.html#TOC59. Additional information on this topic can be found at Microsoft: http://support.microsoft.com/kb/813514

Drawbacks (or notes) regarding a local SMTP gateway

The effort of configuring a SMTP gateway

1. You probably do not need a SMTP gateway if there are fewer than 5 users, however many of the above points remain valid. After 5 users, if the Outlook clients connect directly to OMR the user may intermittently have issues.
2. The SMTP gateway needs to be installed, of course. You should not need to worry about 'creating accounts' if the server is a relay/queue server, because the server will accept any connections from within your LAN.
3. You must take care that the SMTP gateway is NOT exposed to the Internet. This is usually a cursory check: it is likely the server is behind a NAT router and a firewall (and so is not available outside your LAN).
4. Instead of telling your users to set the email client's 'Outbound SMTP' server to 'omr.tzo.com', you would have them configure this setting to '192.168.0.99' (or whatever the fixed-LAN-IP is of the workgroup server.
5. The workgroup server needs to be configured to push the email to TZO OMR, otherwise it will sit in your SMTP gateway's outbound queue. Look for your server's "SMTP Gateway" or "SmartHost" setting - this is where you input "omr.tzo.com".
   
   On some servers this setting does not automatically become "live" meaning you created this rule or 'ACL' but it is not 'enabled'. If your mailserver is like this, you will need to look for the setting to enable the SmartHost rule just created.
6. Cost is not usually a drawback of an SMTP gateway -- many such programs are free or open source, or low-cost 'shareware'. In TZO's Support section, you can find SMTP server tutorials which can serve as a recommendation (such as Argosoft Mail). Because OMR is compliant with all applicable email RFC standards, you can basically use any RFC compliant mail gateway however.