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4

Long waiting for SMTP greeting How long do you wait to get SMTP greeting message? Exact duration in seconds may provide very important hint. AFAIR some servers issue SMTP greeting message after doing DNS lookups (IP address -> DNS name -> IP address). Typical DNS timeout is 75s. DNS is not the only suspect.


4

This problem can be tackled either by postfix or dovecot. In dovecot, you should set the LMTP service to reply with temporary reject 4XX (for your "special" domain) when postfix send email. In postfix, you need to configure postfix so it must defer the email if the recipient domain match your "special" domain. Option 1 isn't possible because -unlike ...


3

There certainly is a difference in how mail servers behave in that case. Ideally the receiving mail server will reject the RCPT command, in which case the mail content will never be delivered to the target server in the first place. In a much less ideal scenario (which is unfortunately often seen in practice anyway), the mail server will accept the RCPT ...


3

The 550 and 553 error codes should all be treated the same by the sending server as will any of the 500 series codes. These all indicate a permanent error condition. The 550 indicates the requested action (add recipient) was not completed. The 553 error indicates that the mailbox name is invalid. In either case the recipient was not accepted.


3

Using option #1 is always the better solution. Think of it like paper mail; a functioning return address is mandatory. Email is only getting more restricted (DMARC, etc) due to spamers taking advantage of the open policy. It's really not that hard to automate dealing with replys you don't care about. But likely less than 10% of email servers are that ...


3

To test an ip in senderbase.org database you have to query their dns server for a txt record with a specially constructed domain name. It should be a sequence of bytes in reverse order representing an IPv4 address, encoded as decimal numbers, separated by dots with the suffix .query.senderbase.org. In your particular case: dig txt ...


2

Use error:nouser 550 ... or error:5.1.1:550 ... as virtusertable value as suggested in virtusertable section of cf/README. info@example.com error:nouser 550 No such user here info@example.net error:5.1.1:550 No such user here RFC5321 describes (subtle) difference between the two error codes. 550 Requested action not taken: mailbox unavailable (e.g., ...


2

SMTPS means SMTP over TLS, like with HTTPS. So first a TLS connection is established (without fallback), and then STMP is started. Just as nobody expects HTTPS on the HTTP-Port 80, you should not expect that anybody who connects to your STMP-service sends TLS requests. Thus, all connections to your server on port 25 will likely fail, if you enforce TLS! ...


2

You are mixing up smtpd_sasl and smtp_sasl, the first is for users authenticating on your server to submit emails for delivery, the latter is used when postfix does not deliver directly but also through a relay and postfix itself authenticates. Unfortunately, when connecting to my server with the username and password, I keep getting authentication ...


2

Most setups include the domain in the username. (At least most of mine.) Try: echo -ne '\0username@domain.com\0password!'|base64 You could also try the PERL approach: perl -MMIME::Base64 -e 'print encode_base64("\000user\@domain.com\000password")'


2

Did you look in /etc/hosts.deny ?


2

Your DNAT rule will route all TCP traffic, received by your KVM host, on port 25, to KVM guest, no matter the interface or destination. You should add either interface or destination IP (or both) in that DNAT: iptables -t nat -A PREROUTING -i your_pub_if -p TCP --dport 25 -j DNAT --to-destination 192.168.122.201:25 or iptables -t nat -A PREROUTING -d ...


1

Your DNS server isn't authoritative for the ip address that your server is using, your ISP is authoritative for the ip address. You need your ISP to create the PTR record for your server in their Reverse Lookup zone.


1

It seems that sometimes your application sends QUIT command before receiving reply for the "the final dot" of the message (250 for OK). It seems that the MTA (MS Exchange) ignores commands received before it sends the reply. Suggested Fixes: 1) Increase timeout for waiting for the reply, do not send QUIT before receiving it (even when PIPELINING extension ...


1

This error Sender address rejected: not owned by user xxx; came from this restriction on submission port (master.cf file) submission inet n - n - - smtpd ... -o smtpd_sender_restrictions=reject_sender_login_mismatch ... As explained in man 5 postconf, reject_sender_login_mismatch Reject the request when ...


1

The shodanshok's comment is right: If you can't telnet the SMTP server, the connection is blocked at the gateway or server level. So I opened a ticket for Digital Ocean's support and got the following response: To curb a recent increase in abuse and SPAM, we have an initial SMTP block on new accounts created in certain contexts. To remove ...


1

Either you or the CA had to create a private/public key pair, before the CA signed the public key. You need the private key in order to decrypt the TLS traffic. If you created the key pair, then you have the private key file. If the CA created it, then they have it and you need to get it from them.


1

You've got Yourself a SSL certificate for your domain, I think you have exported certificate without private key. A ".cert" (or ".cer" or ".crt") file usually contains a single certificate, alone and without any wrapping (no private key, no password protection, just the certificate). Ex- Some CAs store the certificate's private key in a Private Key (.pvk) ...


1

In general, I agree that #1 is probably the best solution, you can just discard any returns at the server. Install a .forward that sends messages to /dev/null. It's unlikely your bandwidth bill will hurt. To the wider discussion as to whether you should care about messages not being delivered, I don't really know anyone processing their own returns at any ...


1

Basically they perform a query for MX record of the domain, following your question, for gmail.com: alphamikevictor@ges01:~ > nslookup -query=mx gmail.com Server: 194.179.1.100 Address: 194.179.1.100#53 Non-authoritative answer: gmail.com mail exchanger = 30 alt3.gmail-smtp-in.l.google.com. gmail.com mail exchanger = 40 ...



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