Overview:
- How does Greylisting work?
- Why is my legitimate e-mail taking so long to get delivered to me?
- What if the external e-mail is still not delivered to me after 4 hours?
- Should I update my personal Whitelist?
- Why am I getting legitimate e-mail in my “Spam” folder?
- Does Greylisting affect e-mail sent from UMBC?
How does Greylisting work?
Essentially any new message, one that has not been seen by UMBC’s mail servers for a period of time, is rejected by our mail servers the first time it is received. Properly configured external mail servers will send the message again, typically twice within the first hour, but some mail servers may wait for several hours before resending. Unfortunately, the “resend” configuration of external mail servers is outside of UMBC’s control.
However, when the second delivery attempt is made UMBC’s mail servers will accept the message and record this in a database. Recording this successful e-mail delivery allows UMBC’s mail servers to deliver future e-mail from that particular sender without first having to reject the message again. The result is that all future mail from that specific e-mail address will be delivered without delays.
This procedure helps to prevent SPAM because spammers typically do not “retry” or “resend” their spam after receiving a failed delivery the first time. They simply move on to the next victim. Therefore, by rejecting the first attempt at delivery OIT can help reduce SPAM on campus.
This is a very brief description of Greylisting. More detailed information can be found at http://www.umbc.edu/oit/news/archives/2006/11/what_happened_t.html
Why is my legitimate e-mail taking so long to get delivered to me?
Greylisting relies on the principle that a properly configured mail server will retry a failed delivery attempt. Unfortunately, not all mail servers are setup the same. For instance, UMBC’s mail servers will retry a failed delivery twice within the first hour. However, some mail servers at external businesses and schools may take 3-4 hours before making a second attempt. The good news is that once the message has been resent, UMBC’s mail servers will allow that particular e-mail address to send mail to UMBC without future delays. Basically the initial delivery delay is a one-time penalty that we endure to help prevent SPAM.
What if the external e-mail is still not delivered to me after 4 hours?
Other servers do not have a well identified fix to make them compliant. For that, the following two procedures exist:
1. Manually perform the "re-send" that the external server should be doing automatically:
a. If it has been a few minutes and the message is not arriving, tell your sender to just re-send the message once to the intended recipient. The recipient might receive 2 copies (one from each send), but the process will not need to be repeated, future messages will pass through without any delay (with only a single sending of the message).
2. Request help in identifying the problem if the above does not work to immediately pass your e-mail:
a. E-mail
b. OIT will extract the information needed from that message
c. OIT will verify the information and see if the problem did or did not stem from a communication with our server,
Should I update my personal Whitelist?
Updating your personal whitelist found at http://accounts.umbc.edu will have no impact on Greylisting. Greylisting does not filter SPAM based on SPAM filtering rules. Instead all e-mail is rejected the first time (See “How does Greylisting Work?”)
However, once the e-mail is successfully delivered your personal SPAM filtering rules and Whitelists will work. This is why you will still see SPAM e-mails in your “Spam” folder. It is also possible that the occasional legitimate e-mail will be flagged as SPAM and placed in your “Spam” folder. Please continue to check your SPAM folder.
Why am I getting legitimate e-mail in my “Spam” folder?
Greylisting does not filter messages based on SPAM filering rules. Therefore, mail successfully delivered to your Inbox will have the same Spam filtering rules applied that we always have. If you find that legitimate e-mail is being placed in your “Spam” folder then you should add them to your personal Whitelist found at http://accounts.umbc.edu or you can simply move them back into your Inbox.
Does Greylisting affect e-mail sent from UMBC?
No, Greylisting has no impact on e-mail being sent from UMBC. It also does not impact mail sent from one UMBC address to another UMBC address.