Place for notes about SMTP
Characters in the local part of the address.
RFC:2821 and RFC:2822 state clearly that only 7bit ASCII characters are allowed in Internet mail addresses.
For a full list of what can/can't and shouldn't be used read this page http://www.remote.org/jochen/mail/info/chars.html
Make sure you've read http://kmself.home.netcom.com/Rants/avspam.html
Unless you can do challenge/response authentication, you should make sure your SMTP server supports SSL as outlined above. The easiest authentication to get working with SMTP is PLAIN or LOGIN authentication.
See EximSmtpAuth for information about configuring Exim for it.
Make sure that your smtp server supports SSL (even if you don't have a certificate), it should do STARTTLS to SMTP servers that support it.
If you use Exim with Debian stable, install the exim-tls package. For Debian testing/unstable (see FlavoursOfDebian), Exim already supports TLS by default.
If you have an SSL certificate, then make sure that Exim knows about it (and that your MXes match the name on the certificate!) so that incoming connections can be SSL encrypted if necessary.
If you relay for other machines, you should set up SSMTP (SMTP over SSL) on Port 465/TCP. This is important in particular for laptops which may be used at a hotel, cybercafe or over wireless where port 25 outgoing may be blocked. MUAs should be configured to use SSMTP where possible.
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