Linux Harbour

Sometimes we received enquiries from our client when one of their business partners/customers could not send emails to them successfully. And we found that the problem is normally caused from opposite Windows email system, which is not configurated well in internet RFC document.

The following line of email reject information is found in email log file.

May 28 17:03:47 mail postfix/smtpd[30547]: NOQUEUE: reject: RCPT from smtp.xxxxxx.com[xxx.xxx.xxx.xxx]: 504 swhkg0111: Helo command rejected: need fully-qualified hostname; from=xxxxxx@xxxxxx.com to=someone@our_client.com proto=ESMTP helo=swhkg0111

It means when this poorly configurated Windows email system (or spammer sometimes) says "Hello" to our client's email system with their non-full-qualified hostname, so the email system is rejected from sending emails to us.

In traditional Linux email server, mbox-format files are used for each user mailboxes, which all incoming emails (eg. in inbox) are stored in 1 files. It is not efficiency to seek for one requested email in a huge mailbox file with many emails, and default size limitation (4GB by default, but it can be changed) of a single file on Linux system.

Starting from 2002, we uses Maildir-format files for email mailboxes on our and our client's Linux email systems. Maildir-format is a file folder/directory for each email mailbox folders (eg. inbox), and each emails are stored in individual files in the same file directory.

We installed a number of Horde IMP webmail on our clients and our own email systems for years. One of our clients reported that sometimes he and his colleagues cannot send emails on webmail.

Recently we googled the problem again, and found a FAQ for Horde IMP matched his problem. It is a problem only occurs to IE users due to security setting of IE/Windows.

MailScanner is a free anti-virus and anti-spam filter running with MTA (Mail Transport Agent) on Linux systems, intergration with other anti-virus/spam software are required to provide these functions.

It highlights on its web site that it may protect over 1 billion e-mails every day, and it got 1 million dowloads. We did a number of Mailscanner installation on Debian and Fedora in past years.