Network Services Group, LLC

Conifigure Greylisting

Question: Why are some of my emails being delayed?

Answer: Probably because of the greylisting spam filter.

Question: Can I turn it off?

Answer: Yes, but you probably don't want to as you will get more spam. See below for more about how it works.

How the greylist spam filter works.

Greylisting rejects emails from people the *first* time they send you an email, and gives the server sending the message a "try again soon message." All legitimate email servers will automatically retry after a short delay. Usually the delay is just a few minutes, but the retry time is determined by the sender's mail server so in some cases it can be longer.

Once they retry the messages are allowed through and the sender is remembered for a month or two, so subsequent messages will not be delayed. The reason this works is because most spammers will not bother to retry — they are too busy sending out tens of thousands of spam mails to other people and most don't want to waste capacity retrying delivery failures.

This really cuts down on spam. You can disable this feature, but you'll get a lot more spam. Or you can whitelist anyone that is adversely affected by it.

Here's what you can do if you don't like it:

  1. Disable the greylisting. We'd advise only doing it temporarily if you are expecting a time sensitive email.
  2. Whitelist the address of the person sending you the email. That will give them a free pass through the spam filter.

More technical details (probably more than you want to know):

Our greylist filter keeps a database of incoming messages and records the sender's email address, and the IP address of the server that sent the message. If someone sends you a message that matches an entry in the database it is allowed through without delay. Otherwise our server will say "temporary failure — try again later" and the sender's server should queue up the message and retry after a short delay. Once the sending server retries, our system will see it in the database and allow it through. This really cuts down on spam.

If this is a problem for you, you can disable the greylisting filter. We'd recommend only doing it temporarily if, such as if you are expecting a time sensitive message, or you'll start getting a lot more spam. Your other option is to whitelist the sender's email address, thus giving them a free pass through the greylist and other spam filters.

With a recent update to our filtering system, now, if a message reaches the stage where it would otherwise issue a greylist delay, it does an SPF query to see if:

  1. The sender domain has a published SPF record
  2. The sending server's IP passes the published SPF policy
  3. There has been a previous delivery attempt from the sender email address to the recipient email address from *any* IP.

If all of those are true, then it will override the greylist delay and allow the message to pass through with a special note in the logs.

Since all of the mega-size email ISPs are savvy enough to publish an SPF record now, this should take care of the issue with mail coming from them. Legit messages from new senders will still hit the one-time initial greylist delay, but you won't run the risk of further retry delays from the same sender on this or future messages.

It also preserves the requirement that we see a previous delivery attempt matching the sender/recipient pair, so a shotgun spammer can't just throw up a "v=spf1 +all" record on a throwaway domain and do a shotgun spam without going through the effort to run a retry-capable mail server — thus the SPF override isn't a get-out-of-jail card for them.

Senders with no SPF records are just processed as they have always been.

Possible filtering of messages out as junk because of SPF violations is something that happens further down the pipeline at the junk filter level.

We are starting to see more and more large email services rejecting mail that come from domains that don't have SPF records, so really, anyone sending you an email from a domain without an SPF record is going to have problems sending email to just about everyone. In other words, if they had things setup correctly on their end, greylisting wouldn't be a problem.

How to Disable Greylisting:

1. Visit https://mail.nsgroupllc.com

2. Type in your email address and password

3. Click the button on the RIGHT that says "Email Options"

Log into NSG Email Options

4. Click "Junk Filter Settings".

Select Junk Filter Settings

5. Scroll down to the greylisting section. You will see a link that allows you to toggle greylisting on or off.

Toggle Greylisting


How to Whitelist an Email Address

Optionally, scroll down further and you can add people to your whitelist. Doing so gives them a free pass through both the greylist and other spam filters.

Whitelist email address
 

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