If you are sending an email to a Kolab Now customer, and find the email delayed or rejected, you may be hitting any of a variety of anti-spam measures deployed on Kolab Now to protect its customers from unsolicited email.

• Email traffic may greylisted, meaning the sending party should re-attempt delivery. This may cause a delay.
• The sending server’s IP address is on a consumer-grade Internet connection, causing rejection.
• The sending server’s IP address reverse DNS lookup does not exist, causing rejection.
• The sending server’s IP address, reverse DNS lookup, sender’s domain or sender’s email address has a bad reputation, causing rejection.
• The sending party or any intermediate infrastructure has already marked the mail as spam, causing rejection.
• The Kolab Now customer’s account is suspended. This results in a delay of up to however many hours or days the sending server wishes to continue attempting final delivery, allowing the Kolab Now customer to pay overdue invoices, then results failure — usually after 5 days, with intermediate notifications sent back to the sender about the delay.
• The email address doesn’t exist and/or is no longer associated with a valid account, causing rejection.
• The email message uses an envelope sender address that is considered a local account hosted with Kolab Now, causing rejection. Customers of Kolab Now should only use submission.

Tags: Tags: Anti-Spam, Greylisting, RBL, RHSBL, Suspension