I am developing a bulk email procedure, in that I have no issues in sending emails in batches. My problem starts when the recipients address is invalid or rejected by the host server.
Simply how can I tell the SMTP server not to retry it the original email was bounced.
I can only use MS Exchange Server.
The number of retries is a setting that you can configure in MS Exchange. See: http://technet.microsoft.com/en-us/library/jj891103(v=exchg.150).aspx
Related
Honestly, I think I have a fundamental gap in understanding how SMTP works. I can't seem to find a good explanation of what is happening behind the scenes and I think this is preventing me from being able to do what I am attempting to do.
To explain, I'm trying to setup an application which sends notifications to users by connecting to an SMTP server. Fair enough. I figure, since I'm using my own domain, I have SPF/DKIM/DMARC configured, I can add an MX record for the host I set the application up on (my SPF record has the mx keyword to authorize any hosts in my MX records to send/receive mails). Then, I can have that same host run a super lightweight SMTP server that can accept mails from the application, and send them on to recipients.
Almost crucially, I want this server to basically just run on localhost so that only this application can connect and send mails through it, but so that it can't really "receive" mails sent to my domain (I have set the MX priority very low (well, a high number) for this app server). I figure since I'm running my own SMTP server, that I don't really need to authenticate against it (it's running on localhost), just take in any mail and send it on to recipient domains.
When sending on to recipient domains... does the SMTP server need to authenticate to say, the gmail SMTP server as a user in order to send mails over there? That seems weird, since it's not a user logging into gmail to send mails, it's an SMTP server that is authorized within SPF sending mail from my domain (From address from my domain as well) to where ever the app server user's email is based (in this example, the user would be e.g., some_user#gmail.com).
I tried using python's aiosmtpd command-line and telnet to send a mail from test#MY_DOMAIN.TLD to test#MY_DOMAIN.TLD and it didn't seem to deliver the message; I figured aiosmtpd would connect to the preferred MX servers for my domain (my "real" MX's) to transfer the message, which would then put it in my inbox. That didn't seem to be the case, and I'm not sure why.
Exact repro steps, where example.com is my domain, and terminals are running on a box with a hostname listed in my MX records.
Terminal A:
$ aiosmtpd -n
Terminal B:
$ telnet localhost 8025
EHLO <example.com>
MAIL FROM: test#example.com
RCPT TO: test#example.com
DATA
FROM: Application Notifications <test#example.com>
TO: User Name <test#example.com>
SUBJECT: App Notify Test
This is a test!
.
QUIT
How do SMTP servers normally send mail between each other? Do they each get some login to each other's SMTP servers to authenticate with, and since I'm not doing that, this is a problem? Can I run a SMTP server on localhost and have it send mail out of the network without receiving mails (a no-reply service)? Is there something obvious that I'm just missing here that solves all my problems?
Thanks
It sounds like you want to run a mail transfer agent (MTA) that relays email to remote SMTP servers. An MTA will typically act as an SMTP server to receive messages, and then it will act as an SMTP client when it relays the messages to remote hosts.
MTAs generally operate in two different modes: (1) They will relay messages from authenticated users to remote hosts, and (2) they will receive messages from remote hosts to its users and store them somehow. The combination of those two modes - where the MTA will accept messages from remote hosts and relay them to different remote hosts - is called an open relay and is sure to attract spammers and place your server on spam blacklists.
aiosmtpd is not an MTA or an email relay out of the box - it is merely an SMTP server that will receive messages and do whatever with the messages you program it to do. By default it will do nothing - that is, it will receive the messages and throw them away. If you want to implement an email relay in aiosmtpd, then you need to implement the SMTP client portion of the MTA, e.g. by implementing an aiosmtpd handler that instantiates smtplib.SMTP to connect to remote hosts.
However, if all you want is an email relay, then you most likely don't need aiosmtpd at all - postfix is probably a better choice.
aiosmtpd can be a good choice if you need to implement mailing list software or perform some automation tasks based on incoming emails from e.g. cameras or scanners.
If you want to implement an email relay in aiosmtpd, then you need to ensure that both the software and your server are configured in a way that you don't relay unauthenticated messages from the outside internet.
See also: Python aiosmtpd - what is missing for an Mail-Transfer-Agent (MTA)?
So, I actually figured out what was missing here.
I need to run an SMTP server, yes, but I also needed to write code to parse the "to" domain (the recipient domain), perform a DNS request for the MX server(s) of the recipient domain, and then use the smtplib client to then send mail over to the recipient domain. Authentication is not needed to relay that message to the recipient server, authentication is only required for reading from a given inbox or authenticating a sender to send on behalf of a domain (I trust myself and myself only to send mail). I can do all this while also only listening for mail on localhost so that only my local server can use the local SMTP server for relaying messages/emails off to recipient domains.
Additionally, I don't need to have my external IP listed as an MX server since it's not accepting mail for the domain, only sending. I do need an SPF record for it though so that it is an authorized relay/sender for email from my domain.
I'm trying to implement a SMTP server at the moment and I've question regarding the routing...
Imagine, a client (foo#bar.com) sends a mail to foo1#bar1.com, foo2#bar2.com and foo3#bar3.com.
What happens when the SMTP server sees the message? Now, I'm not sure if the following sequence is correct:
The SMTP server will put the mail into the outbox of foo#bar.com
For each recipient (except foo#bar.com) in the envelope, the SMTP server will do:
Retrieve the MX record
Connect to the SMTP server determined by the MX record
Send HELO/EHLO command
Send MAIL FROM command (foo#bar.com)
Send RCPT TO command (e.g. foo1#bar1.com)
Send DATA command
Send QUIT command
Are these steps correct? For me it makes sense that the SMTP of the sender processes all the communication, but I've found some pages (e.g. https://www.msxfaq.de/internet/envelope.htm) where a mail server only forwards the message to the next SMTP server and each SMTP server removes one recipient from envelop's rcpt-to list, e.g.
So, what's correct...?
Sender's SMTP handles all the routing
Sender's SMTP removes one recipient (in this case foo#bar.com) and then forwards the message to the next SMTP server
The steps you listed are basically correct.
The complexity arises when you compose an email and try to send it to a lot of different domains, e.g. steve#apple.com, woz#apple.com, and bill#microsoft.com.
In this case, the server must do MX lookups on each one of these domains and split the email. Steve and Woz are both at the same domain, so the server can send an email with those two recipients to the MX record for apple.com. The server must open a separate connection to the MX record for microsoft.com and attempt to send the email to Bill over that connection.
I have a Coldfusion page (CF10) that creates a report and sends it via cfmail to a list of recipients. The ones in our internal domain are receiving, but the external addresses are not.
I found a couple threads where people were having the exact same problem, and the solution was to add the CF server's IP address to the Exchange server. So our IT guys did just that - they added the IP addresses of all of our production servers to the receive connector on the Exchange server. However, the mails are still not being relayed, and I'm continuing to get the same message in the mail log:
javax.mail.SendFailedException: Invalid Addresses; nested exception is: com.sun.mail.smtp.SMTPAddressFailedException: 550 5.7.1 Unable to relay
I'm not familiar with everything that needs to happen to make the Exchange Server relay email to external addresses. Adding the IP addresses to the receive connector obviously isn't enough. Are there other steps that need to be performed?
Coordinate with your IT guys. Write a ColdFusion page that they can run that sends mail to an external address they can access. Then tell them to do what they have to do to receive mail at that address.
Solution was simple - we originally specified the mail server in the cfadmin mail settings, but included no username/password. That worked fine, until we wanted to start sending cfmails to addresses outside of our own domain. So IT created a dedicated "Noreply" account for this purpose, and I entered the username/password in the cfadmin mail settings.
Do the SMTP logs on a server (Windows 2003) only show logs of mail that were sent successfully?
We are getting bounce backs when sending mail to a particular domain:
The connection was dropped by the remote host.
It looks like a problem on the receiving server, but we dont have much information to provide them. We can send to hotmail, gmail, yahoo etc OK.
Any ideas?
Most likely, there is a spam filter in front of the receiving mail server for this domain, and this spam filter thinks your mail server is sending spam, so it's closing the connection from your mail server. One way to test this is to simulate sending a message to this mail server by opening a command prompt on your mail server, and use telnet to connect to the receiving mail server on port 25, and proceed with the process of sending a message just as a mail server would. This way, you'll be able to see how the receiving mail server responds after each step. Follow the instructions in http://support.microsoft.com/kb/153119 to see how this is done.
It turned out the sending server was blacklisted by McAfee, that was running on the receiving servers firewall.
For those that may have the problem in the future you can check if your server is blacklisted with McAfee here:
http://www.mcafee.com/threat-intelligence/ip/spam-senders.aspx
After entering your server IP, you should see a link Threat Feedback. Use this to email McAfee.
I was able to send McAfee an email with an explanation, they then removed our server from the blacklist.
I would like like guidance regarding an issue we are having on our CentOS server.
Just recently we noticed that we cannot send emails to Hotmail.com mailboxes from our domain email. I also discovered that we're getting a lot of mail delivery failure emails in one of the inbox's that we don't use.
I've checked the mail logs and saw some suspicious activity. Unfortunately, I don't know much with regards to mail server and how they behave. Can someone shine some light on this situation and tell me if some is connecting to our SMTP server remotely and sending spam emails to various recipients? What other steps should I take to prevent this?
Here is part of the log:
2013-06-09 05:43:27 SMTP connection from [110.52.1.237]:13088 (TCP/IP connection count = 1)
2013-06-09 05:43:32 no host name found for IP address 110.52.1.237
2013-06-09 05:43:41 SMTP connection from [110.52.1.237]:13461 (TCP/IP connection count = 2)
2013-06-09 05:43:46 no host name found for IP address 110.52.1.237
2013-06-09 05:43:46 unexpected disconnection while reading SMTP command from (iem.net) [110.52.1.237]:13088
2013-06-09 05:43:55 H=(qbnngj.com) [110.52.1.237]:13461 sender verify fail for <wqnsjzyyc#qbnngj.com>: The mail server could not deliver mail to wqnsjzyyc#qbnngj.com. The account or domain may not exist, they may be blacklisted, or missing the proper dns entries.
2013-06-09 05:43:55 H=(qbnngj.com) [110.52.1.237]:13461 F=<wqnsjzyyc#qbnngj.com> rejected RCPT <support#greenXXXX.com>: Sender verify failed
2013-06-09 05:43:55 unexpected disconnection while reading SMTP command from (qbnngj.com) [110.52.1.237]:13461
As you can see above, the IP that connected to the SMTP server is from China. I have a dozen of similar connections made in the log.
I am not sure how to resolve this issue.
Any help would be appreciated.
Thank you,
Max
You have two separate problems.
Sending to Hotmail: They have a web page regarding their own private white list, and if you're not on the list, you get blocked.
Receiving delivery status notices for messages not sent: Someone is spoofing your domain in messages they're sending to others. You need to protect your domain with some authentication technology. The two most common are called "sender policy framework" and domainkeys.