Luke Dudney wrote:
There are lightweight SMTP clients that can be used as drop-in sendmail(1) replacements by speaking directly to a remote SMTP server instead of dropping the message in the local queue directory. One that I've used is mini_sendmail (http://www.acme.com/software/mini_sendmail/), though this was a while ago but I seem to recall having some success with it.
Others have mentioned the trade-off between the additional complexity of maintaining an MTA on each system and the fault-tolerance such a setup provides, however, you can achieve similar levels of fault tolerance by implementing redundancy on your relay server system(s). I guess it's up to you to figure out what's appropriate to your environment.
it's not a redundancy issue. it's a queue issue. when cron sends mail and if the sendmail command fails, cron can't do anything (it won't queue mail and retry later).
That said, one can write a script (perl comes to mind) or program that: - replaces sendmail - tries to send, and if it fails saves the message in a queue - runs periodically (from cron for example) to check the queue
but I am not convinced that setting this up on every machine would be easier than configuring postfix or sendmail as a "null client".