SMTP Restrictions

Our upstream providers have placed restrictions on their SMTP servers in order to prevent abuse. These limits are as follows:

Limitations in place on smtp-is.zsd.co.za and smtp-za.zsd.co.za

Policy:

• The end user can only send to a maximum of 100 recipients per mail message, this includes To:, Cc: and Bcc:.
• The size limitation is 102.4 Mega Bytes per message.
• Relaying is only allowed from IS DSL ip ranges.
• The sender and recipient domains must be a Fully Qualified Domain Name and be a valid resolvable DNS domain.
• No sender From: addresses from free mail services, i.e. Yahoo, Hotmail, GMail, etc are accepted.
• Testing for open relays on the IS DSL user ip space and blocking access to these abusers.
• Blacklisting and block ip's identifying themselves as one of the smtp servers.
• Blacklist ip's sending mail to known spam traps for a minimum of 1 hour.
• Manual process of blacklisting domains and/or sender addresses due to abuse complaints being logged.
• Rate limiting incoming mail from client connections to 50 recipients max per minute.
• Rate limiting incoming connections from client connections to 7 per unique ip on each server.
• Reject any mail that has more than 50 MIME parts.
• Reject any mail considered to be malware infected.
• Reject any mail looking like spam.

Technicial Policy:

• Max recipients in a single connection - 100
• Max mail size including the encoding of the mail - 100MB

• 7 Concurrent connections per server. Total concurrent connections -> 28

Limitations in place on smtp-sx.zsd.co.za

• 25 recipients per message
• 250 MB traffic per hour
• 300 recipients per hour
• 1000 recipients per 24 hours
• Users are not allowed to send to 3 or more AOL, Yahoo or Hotmail email accounts in the same email.

Hosted Exchange policy document