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Questions tagged [smtp]

SMTP is the Simple Mail Transfer Protocol, the most recent standard of which is defined in RFC 5321. It's the Internet standard for sending and receiving email.

Some characteristics of SMTP (Simple Mail Transfer Protocol):

  • The default port is TCP port 25 and new submissions (MSA) is port 587.
  • Although depreciated, some services still use port 465 (SMTPS) to support legacy applications.
  • It is used to transmit outbound mail, and mail servers (which listens on port 25) receives mail on port 25.
  • It should not be confused with POP3 / IMAP which is an actual store for the e-mail. SMTP messages are received by the receiving server and then an MTA moves it to the POP3 / IMAP mailbox where it is normally retrieved using a POP3 / IMAP client.

See Also:

RFC5321

3133 questions
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Exchange (therefore Outlook too) don't recognize senders on messages originated over SMTP

I have an application that needs to send (internal) e-mails, so naturally it uses SMTP. Our e-mail server is Microsoft Exchange. When I look at the e-mails in Outlook, something isn't right with the Sender address. It appears as a proper SMTP…
Adam Batkin
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How to correctly manage multiple virtual hosts with postfix?

I'm tring to correctly setup a postfix server for our products for a couple of days. The server is running correctly but some emails sended to gmail are delivered to spam box. The server is configured like this: /etc/postfix/main.cf mydomain =…
Gardner
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After changing SMTP port from 25 to 587 I can send, but now I don't receive emails

I configured Postfix, after a time I discovered I am blocked from sending emails because my network is on a blacklist (it's a dynamic IP). So, sometimes Outlook does not connect to send (still gets the mails). Then I changed the SMTP on the master…
user156355
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Resolving CloudFlare DNS related mail delivery problems

I recently started using CloudFlare and am having a few teething problems. Our domain is netlanguages.com and while we have a lot of sub-domains listen, we are currently only trialling a few of the servers through the CloudFlare CDN (for example,…
Andy Castles
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Postfix: throttle incoming traffic to abused recipients

I'd like to implement per-recipient limits for incoming mail to our Postfix MX servers, but I don't know what to use to achieve that. Postfix docs and Google searches will only give me config recipes to set up (global) incoming concurrency or…
Luke404
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Telnet to SMTP gets no 220 response unless user is specified

My server is setup to generate outgoing email only (no receiving), and is timing out when attempting to contact smtp.example.com Essentially the email is generated by a process on myserver.example.com, sent to postfix on the localhost, which acts as…
Andrew Parker
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Using a local MTA as gateway to Sendgrid

I am setting up an email system using Interspire Email Marketer with 5 user accounts, and each user has their own Sendgrid account. We are trying to build a fast system, so we have a dedicated MySQL server with lots of RAM, a web server to host the…
Charlie
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Email sent via SMTP server - working except to our Exchange account?

We currently have a server set up as an email sending box. It has a Windows Service setup to periodically send emails through an SMTP server which is configured on the same box. The service and SMTP server are generally working fine, as I can send…
stevehayter
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how to receive emails on linux?

Is there any small utility to receive emails on linux ? Ideally I would need to point mx records on my server and through just a command read all the emails received. I don't need pop3, imap, any user account management, database etc ... basically…
Doing Things
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Is forwarding mail from my domain to my gmail account a bad idea?

I just configured my exim mail server to forward *@mydomain.com to my gmail account. But then I found some forums mentioning this is a bad idea. Google could eventually blacklist mydomain.com. Is this really a bad idea? I guess there is…
Eric Johnson
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Exchange 2003 - is mixed authentication possible (user/pwd & whitelist IP)?

I am working with a client who has user/password authentication in place for their Exchange 2003 server. However, the application I am assisting them with will be running on a server inside their network, and is having trouble with user/password…
irCristos
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csf/lfd parameter that prevent smtp attacks?

I have a 4~5MB logwatch like this every day! someone like to hack my smtp: .... --------------------- sasl auth daemon Begin ------------------------ SASL Authentications failed 3965 Time(s) Service smtp (pam) - 3965 Time(s): Realm - 3959…
exim
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What protocol does Exchange use to relay email to other Exchange servers?

Suppose an organization has multiple Exchange servers. These Exchange servers can use SMTP to relay email to each other. In this case, they would probably use some Exchange-proprietary extensions, such as XEXCH50 and X-LINK2STATE. Question: Is…
james.garriss
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Is it common for e-mails to get rebuilt during transmit?

I'm having a problem where some user's of my web site complains they're receiving empty e-mail messages. After comparing the content and e-mail header of their e-mails with the ones I get I'm leaning onto the conclusion that their mail server…
m__
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Postifx: how can someone send e-mail without authorization with this configuration?

Yesterday I found that 10 thousand e-mail messages were sent through my system using this configuration: http://pastebin.com/bThpH1s8 - main.cf http://pastebin.com/kkxxsstP - master.cf I temporarily blocked the whole spamer's ISP's IP range, but…
Ernestas
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