503 Bad Sequence, polite people say HELO first

If you ever get an email that fails to send with a 503 error, it doesn't mean that you should add 'HELO Bob' to the start of your email and try resending it. The 503 error actually means that your mail server is not behaving properly or that something is wrong when trying to send your email. The latter part of the message is simply the other mail server trying to be cute.

For those of you that are not aware of how mail servers work, here is a brief explanation of how they communicate. Before your mail server could relay your email, it first have to introduce itself by saying HELO. For the more trendy servers, EHLO works too. If you're bored, scream NOOP, NOOP and the other server will merrily reply OK, OK. (Having said that, I don't guarantee that prolonged NOOPing will not upset the other server, prompting it to sever all connections with you.) If you're ever in need of assistance, just ask for HELP and you'll get an appropriate response.

That's the humorous world of digital communication for ya! If you seriously want to learn more about how mail servers communicate (or if you're looking for a cure for insomnia), then have a read thru the following.

RFC2821 - Simple Mail Transfer Protocol