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hints:mail_forwarding [2021/02/19 05:51]
admin [Mail forwarding problems]
hints:mail_forwarding [2021/03/08 09:41] (current)
admin [Mail forwarding causes backscatter]
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 Whichever mail forwarding method you use from below, always test. Send yourself mail from some outside service and check to make sure it got forwarded as expected. This will help prevent silent loss of mail, where mail gets accidentally forwarded into oblivion, or even to the wrong person. Whichever mail forwarding method you use from below, always test. Send yourself mail from some outside service and check to make sure it got forwarded as expected. This will help prevent silent loss of mail, where mail gets accidentally forwarded into oblivion, or even to the wrong person.
  
-====== Backscatter caused by forwarded spam ====== 
  
-When you forward mail, unless you use procmail, spam will be forwarded. The receiving site may reject the spam, causing the forwarded mail to bounce back to the original sender. If the sender address was forged, this will cause the bounce to go to some innocent party. This type of bounce is called [[hints:backscatter]]. Excessive backscatter from our servers may cause us to be added to block lists, causing **all** mail originating from the server fail. 
- 
-For this reason, if you receive any noticeable amount of spam to an email addresses, you should forward mail arriving for that email address only by using procmail, and using our [[hints:example_procmailrc_file_forwarding|example .procmailrc file for mail forwarding]] to block most spam from being forwarded. 
- 
-In the [[:Classic Linux]] environment, if you use the **mailq** command and find any significant amount of queued mail that seems to be to you or from you, quite likely this is backscatter being generated by mail forwarding that you are doing. 
 ===== Mail forwarding with a .forward file ===== ===== Mail forwarding with a .forward file =====
- 
-**Forwarding mail with a .forward file will forward spam.** 
  
 You can create a **.forward** file in your home directory. Incoming mail for your primary Linux login (**USER@rahul.net**  in Classic Linux, or **USER@jade-new.rahul.net** in DirectAdmin) will be automatically forwarded to any address(es) found in the .forward file. These addresses can be on a single line in the .forward file, separated by commas, or one per line without commas.  These are examples of syntactically valid .forward files: You can create a **.forward** file in your home directory. Incoming mail for your primary Linux login (**USER@rahul.net**  in Classic Linux, or **USER@jade-new.rahul.net** in DirectAdmin) will be automatically forwarded to any address(es) found in the .forward file. These addresses can be on a single line in the .forward file, separated by commas, or one per line without commas.  These are examples of syntactically valid .forward files:
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 ==== Mail forwarding with a .forward file and keeping a copy ==== ==== Mail forwarding with a .forward file and keeping a copy ====
- 
-**Forwarding mail with a .forward file will forward spam.** 
  
 To forward but also deliver into your normal mailbox, include your Linux login name as a forwarding recipient, but prepend a backslash to it. Examples are below. USER stands for your own Linux login name. To forward but also deliver into your normal mailbox, include your Linux login name as a forwarding recipient, but prepend a backslash to it. Examples are below. USER stands for your own Linux login name.
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   * [[hints:procmail_classic_linux|Procmail mail filtering in Classic Linux]]   * [[hints:procmail_classic_linux|Procmail mail filtering in Classic Linux]]
   * [[hints:procmail_directadmin|Procmail mail filtering in DirectAdmin]]   * [[hints:procmail_directadmin|Procmail mail filtering in DirectAdmin]]
-  * [[hints:example_procmailrc_file|Hint: example .procmailrc file]]+  * [[hints:example_procmailrc_file|Example generic .procmailrc file]]
  
 ===== Mail forwarding from within your control panel ===== ===== Mail forwarding from within your control panel =====
- 
-**Forwarding mail from within your control panel will forward spam.** 
  
 You can set up mail forwarding from within your [[:Virtualmin]] or [[:DirectAdmin]] control panel. You can set up mail forwarding from within your [[:Virtualmin]] or [[:DirectAdmin]] control panel.
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 ===== Mail forwarding causes backscatter ===== ===== Mail forwarding causes backscatter =====
  
-Almost all incoming mail includes some amount of spam. Our servers typically reject about 80–85% of all incoming mail because it is diagnosed with high confidence as spam. The 15–20% that is permitted to reach you includes some fraction that is likely spam. Mail forwarding as enabled within the Virtualmin control panel, or as enabled using a '' .forward '' file, will include some small amount of spam.+Almost all incoming mail includes some amount of spam. Our servers typically reject about 80–85% of all incoming mail because it is diagnosed with high confidence as spam. The 15–20% that is permitted to reach you includes some fraction that is likely spam. Mail forwarding as enabled within the Virtualmin or DirectAdmin control panel, or as enabled using a '' .forward '' file, will include some small amount of spam. 
 + 
 +If the site that receives this forwarded mail detects spam and rejects it, that will become a delayed bounce that our servers will try to return to the original sender. But in most spam, the sender is forged. The bounce will therefore go to some innocent person. This is called [[backscatter]]. Excessive amounts of backscatter may be treated as a type of spam coming from our servers. This may cause our servers to be added to various black lists, causing outgoing mail from our servers to be blocked, and thus causing inconvenience to all users. 
 + 
 +In the [[:Classic Linux]] environment, if you use the **mailq** command and find any significant amount of queued mail that seems to be to you or from you, quite likely this is backscatter being generated by mail forwarding that you are doing. 
 +====== Mail forwarding solutions ====== 
 + 
 +There are a number of possible solutions. 
 + 
 +===== Discarding bounced spam automatically ===== 
 + 
 +Our servers try to detect bounced spam and discard it. This works if the rejection message from the receiving site appears to indicate that the site rejected the message because it was diagnosed as spam. This type of bounce is then simply discarded, and does not become backscatter. 
 + 
 +If a receiving site rejects mail as spam but our system doesn't recognize the error message, then it will try to return the bounce to the original sender, and the message will then become backscatter. 
 + 
 +===== Having the receiving site pull mail from your mailbox ===== 
 + 
 +A second solution is to have the receiving site pull mail from your mailbox directly, so you don't have to forward it. Many email sites will fetch your mail from our servers via POP, if you give them your login information. Only **if** you trust such a site with your login name and password, then this mechanism is preferable to normal mail forwarding. Then:
  
-If the site that receives this forwarded mail detects spam and rejects it, that will become bounce that our servers will try to return to the original sender. But in most spam, the sender is forged. The bounce will therefore go to some innocent person. This is called [[backscatter]]. Excessive amounts of backscatter may be treated as type of spam coming from our servers. This may cause our servers to be added to various black listscausing outgoing mail from our servers to be blocked, and thus causing inconvenience to all users.+  * Your mail will be safely fetched regardless of a sending domain's SPFDKIM, and DMARC records. 
 +  * Mail fetched in this manner will not become bounced backscatter.
  
-====== Mail forwarding solution ======+===== Combination solutions =====
  
-Many email sites give you an alternate mechanism. They will fetch your mail from our servers via POP or IMAP, if you give them your login informationOnly **if** you trust such a site with your login name and password, then this mechanism is preferable to normal mail forwarding. It does not suffer from the spam problemYour mail will be safely fetched regardless of a sending domain's spam policies.+One slight disadvantage to having a receiving site pull mail from your mailbox is that there may be a slight delay, of a few minutes, before incoming mail reaches the destination siteA good combination solution is to use **procmail** to forward mail, while not forwarding spamThis makes your mail reach the forwarded destination immediately. Any mail not forwarded because it might be spam is then pulled from your mailbox by the destination site within a few minutesAlmost all mail will be directly forwarded, and any that is not will be pulled via POP. Forwarding with procmail is discussed earlier in this document.
hints/mail_forwarding.1613742681.txt.gz · Last modified: 2021/02/19 05:51 by admin