Orion cannot buffer alert emails actions.
Here is what you can do instead:
A work around would be to install a lightweight SMTP server on Orion such as hmailserver (http://www.hmailserver.com/) and to configure a DNS round robin name (http://en.wikipedia.org/wiki/Round_robin_DNS) which will failover to the Orion server if the SMTP server is not available.
Once done, configure your alerts to use the newly configured domain named as the smtp server.
Note that you can configure your alerts to write an event into the NPM Event Log to keep a trace of which alert has been triggered/reset.
I am searching for a solution for this, but I would want to send a SMS alert instead...
Yes you can do SMS with Orion. You have to buy a thrid party program Notepager. http://notepager.com/
Once you buy and install the program you have to set up the notepager with numbers to dial and what not. You can choose between a SNPP protocol or POTS which you will need a modem hooked up to your server for. Currently I run all of my SMS messegase over SNPP over IP as long as the servers internet connection is up. I have a conditional alert that if any nodes between my server and the internet connection go down it dials out for alerts.
Once you have all that set up it is as simple as making an alert with the SMS action selected.
We saw this problem also so we built a program that can send sms from a command line through a gms-modem connected to the orion-server.
If everything but the orion-server i down we can still get the alert.