In an ideal world all the services are running, all machines are up,everyone behaves normally, there is no dissent, nobody wishes to steal your money and nobody lies and so on.
But reality is very different from this. Machines go down, there are ISP outages, cable cuts, volcanic eruptions, power cuts, cable pulls and WiFi outages, password leaks, auth key mismatches, many things can go wrong, by Maslow's law if you will.
So to make things smoother for you and for us, SpamCheetah came up with this unique feature of temporary Queuing of mail when your target mail server goes down in Standard edition. Usually such events do not last very long and they get corrected very quickly but till such time mails are not bounced but saved in SpamCheetah's internal secondary storage. Once mail server is back online SpamCheetah resumes its normal proxying operation or greylisting depending upon which mode it was setup.
The feature of queueing mails automatically once mail server is detected to be down for some time is to be interpreted as an emergency measure, so mails are accepted without spam or virus checks. Please fix your mail server or connectivity quickly so spam control, URL and malware filtering can occur as per your license.
Temporary mail queuing is active only when target mail server is down in standard edition. This feature does not apply to heavyduty edition since there is no need to queue mail temporarily. All mails are queued anyway.
To have to use temporary queuing there is no need to enable anything , setup anything on web interface or contact us. It is enabled by default and by the time we alert you by email that your mail server is down very likely the temporary queueing is already enabled.
You can check it by accessing the licensing page of the web interface, screenshot below. If the mode shows pass thro' it means that your mail server is down. And queueing is in action.
Please scroll to bottom of the page. You also find it in top line display in the dashboard. Anyway as this is a stop gap arrangement you should realize that getting the mail server up is your first priority and things may deteriorate if things are left like this since there is no spam control and SpamCheetah cannot store large qualities of mail if yours is a busy site.
Temporary mail queueing is a way to temporarily store mail inside SpamCheetah by redirecting SMTP traffic to the internal mail server during moments of the mail server being down.
SpamCheetah is acting as an SMTP proxy that sits between external mail senders and internal mail server the receives all the e-mail traffic. In case due to some reason the internal mail server is found dead/unresponsive then SpamCheetah takes action.
This is what SpamCheetah does in short.
The above schematic and details must explain the most important aspects of this feature. Some more elaborations here.
Instead of sending a bounce to the external mail senders, SpamCheetah tries to do its best to react to emergency situations. But if the mail server is down for long then there could be disk space issues in SpamCheetah and mails and spam service can both fail.
So you must use this feature only as a temporary safeguard against mail server outages. Since SpamCheetah alerts the admin, it is likely the mail server is restored ASAP.
The mail server being back is checked every 2 minutes of 120 seconds.
With this feature no bounce message is sent when your mail server experiences an occasional outage.
It is possible to get mails delivered once the target mail server comes back.
Some of the mail filtering features may not work in this period. Since pass thro' mode by definition means that your mail is simply accepted as is without any proxying or scanning no virus scanning or malware check or attachment filtering or sender or recipient blocking works in this mode.
Also an email alert is despatched by SpamCheetah the minute the mail server is discovered to be unresponsive.
It is not likely that SpamCheetah will run out of disk space since once the mail server is up the mails are delivered immediately and space is reclaimed but you can speed things up by reacting quickly and checking our live dashboard on top right corner to check disk usage. Screenshot below.
You cannot count on proper behavior of SpamCheetah if things go out of hand like disk fills or mail server is down for too long. But in most cases there is no need to panic. If things deteriorate simply power cycle SpamCheetah using the web interface or physically after restoring mail server state.
Please use this feature with caution as this is not an ideal case. Only a stopgap arrangement to help exigencies.
The ability to function normally in emergency situations is already built into the SMTP at the protocol level due to its queuing feature and bounces are sent only after multiple attempts, so it is very unlikely anybody is going to know about transient outages as long as things are reacted to, alert mails configured and read and so on.
Depending on the traffic at your site the outage could become more serious over time. In most average traffic scenarios there should not be cause for alarm though.
If it takes time to fix the mail server reachability then if you have configured backup MX things could be queued up there. Or senders will start seeing bounces. At any rate temporary queuing is only temporary as the name itself suggests.
Another architecture is to setup a backup MX or switch priority or something. Clustering is another choice too. SpamCheetah's clustering feature is still under development, but most cloud providers provide redundancy clusters and you could use that if you wish.
If you are unable to resolve satisfactorily you can of course go for the heavyduty edition of SpamCheetah which means the queueing is part of the appliance itself. That however implies you install SpamCheetah on large disk space gear or VM.
The mail server that powers your site in standard edition is always expected to be up and running and they can be colocated or in a different continent but it must at all times be reachable by SpamCheetah since SMTP proxying happens at a very deep level and without a live mail server SpamCheetah is like a toothless tiger.
No amount of planning or work can change that work. So ensuring your mail server connectivity must be of utmost concern. As we discuss in one of our blogs about mail servers plenty of really high quality mail servers are available today in both free/gratis/open source world and as commercial products. It is usually spam control that scares people from installing their own mail server. But mail server administration is trivial as long as your IP address is not listed in RBL lists.
And you take extra pains to ensure that your mail server reputation is kept sacrosanct at all times by not sending campaign mails or misconfiguration as open relays or something.
Your age of the domain also matters for reputation and new domains take time to warm up before your mail server gets good sender score.
The way SpamCheetah can help is quickly setup your mail server and configure spam control but the external mail sending path is not in SpamCheetah's hands and if you have a compromised machine in your network then you could be in trouble. So you must maintain your mail server and monitor its IP and domain reputation often just like you monitor SpamCheetah graphs and reports.