When at all possible, send mail through our mail hub. In the past, you could send from arbitrary machines, but the self-appointed spam police of the world have decided that mail for a domain originating from multiple locations is a sure sign of spamming. Additionally, it is highly likely that your ISP's entire netblock has been blacklisted already. If you are using your hcoop.net address you must send mail through us because our SPF records mandates it in order to reduce the likelihood Google et al will flag our messages to members as spam.
Configure mail.hcoop.net as the outgoing SMTP server in your mail client. You can use either port 25 or port 465. You must enable TLS SMTP auth, and you will need to authenticate with the same username and password that you use to get mail from POP3 or IMAP. Virtual mailbox names and passwords may be used here. The server will not query you for a username and password by default. Thus, you will get confusing error messages if you don't configure your client to attempt to authenticate with plaintext SMTP auth using TLS.
The SMTP server requires a TLS aware mail client. MacOS X <= 10.6 Mail, Outlook, and Opera do not seem to support this at the moment. Mozilla supports TLS and runs on MacOS X, Windows and Linux. Mail on OS X 10.7 (Lion) supports TLS for SMTP, but it must be configured using the account preferences dialog rather than the initial account setup wizard.
You may also want to reconfigure your domain to use addDefaultSPF which sets an SPF record indicating that all mail for your domain will go through our mail servers (more generally, any mail exchanger you've set). If you ever send mail from another host by changing the From, you do not want to do this as it would increase the likelihood that mail is marked as spam.
ISPs that block SMTP
Some ISPs and possibly other networks discriminate against the SMTP protocol. Some block or filter in or outgoing SMTP altogether.
If you need to send mail using HCOOP's mail server and experience long delays, this is likely due to your network. You can test out the mail server's responsiveness by doing "telnet mail.hcoop.net 25" on both your local machine and ssh.hcoop.net. If you immediately get a "220" banner, the server is working fine and you can type "QUIT".
To work around this issue, you can use mail80.hcoop.net as the server, and configure your email client to send mail through port 80.
Mail clients that don't understand TLS
You can also set up a custom SSH tunnel to port 25 on ssh.hcoop.net, if your MUA can't/won't use TLS.
Configuring programs to send mail through HCoop
For information on how to send mail through HCoop's SMTP server, check out our SMTP Clients subpage.