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CSmtpProxyMT 1.0

, 15 Nov 2001 CPOL
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An SMTP proxy class with ability to insert signatures to outgoing mails. Does not require MFC.


CSmtpProxyMT is a C++ class that provides developers with a simple way to implement a multi-threaded SMTP proxy server in their applications. You can use it in MFC projects as well as in non-MFC C++ projects. I'd like to thank my good friend Colin Davies for his idea of inserting signatures into mails at the SMTP level instead of at the mail client level.


  • Simple C++ interface
  • The code does not use the MFC Socket classes. Thus it avoids several pitfalls associated with the MFC Socket classes
  • You can use it in MFC/non-MFC applications as well as in console applications
  • Multithreaded [uses the CRT function _beginthreadex instead of the API functions]
  • Ability to insert a signature to all outgoing mails [html mails, text mails, mails with attachments]
  • You can create CSmtpProxyMT object only on the heap. If you attempt to create the CSmtpProxyMT object on the stack, you'll get unpredictable results.


  1. Add SmtpProxyMT.cpp and SmtpProxyMT.h to your project

  2. Put #include "SmtpProxyMT.h" on top of your source file, from where you wish to instantiate the class

  3. Add WS2_32.lib to the list of Library/object modules

  4. Add a member variable to your class or if you are not using a class, simply declare a member variable as follows :- 

    CSmtpProxyMT *m_smtpproxy;

  5. Now create the object either in your constructor or somewhere similarly suitable :-

    m_smtpproxy = new CSmtpProxyMT;

  6. You can also set the signature to be attached to all outgoing mails

     m_smtpproxy->SetSignature("Hello World from Nish");

  7. Starting the proxy is easy :-


  8. You can stop the proxy just as easily :-


Function Reference

I'll list below the public member functions that you can use



Remarks :- Constructs a CSmtpProxyMT object. Please remember that you should only create the CSmtpProxyMT object on the heap.


int StartProxy(char *server, int port, int localport);

Return Value :- This will return ERR_RUNNING if the proxy is already started. Else it will return OK_SUCCESS

Parameters :-

server - You specify the SMTP server here. You can use a domain name such as or you can use an IP address such as

port - This is where you specify the SMTP port, usually 25

localport - This is the SMTP proxy port. You can specify 25 here too, unless you are running the proxy on the same IP as the SMTP server. In that case use something else.

Remarks :- This will start the SMTP proxy service. Currently if there is a host resolve problem you will not get notified. This is a TODO for me.


int StopProxy();

Return Value :- This returns ERR_STOPPED if the proxy is not running. Otherwise it returns OK_SUCCESS

Remarks :- This stops the SMTP proxy service.


BOOL SetSignature(char *sig);

Return Value :- This will return true if the signature was successfully set. It will return false if the signature is too large.

Parameters :-

sig - This is used to specify the signature. It should be a null-terminated string.

Remarks :- Currently there is a 2 KB limit which can be easily modified by editing the source. This version supports only text signatures. It's a TODO for me to add HTML signature options in the next version


  • Colin Davies - For the signature idea

Some remarks

I am sure purist C++ programmers will frown on seeing my source code. I have not followed strictly  proper coding standards nor have I tried to stick to perfect OOP concepts. There might be people who say, that this is not the way to write code. Well, that's the way I write code. Perhaps I need to change, but it's not going to be easy

I have tested the class using Outlook Express 6.0. I have tested it with several combinations such as text only mails, html mails, mails with single/multiple attachments. So far I haven't had any problems. But I presume that there might be problems with some mail clients that use their own methods in sending mails.

You'll also notice that I haven't commented the code much. But the code is self-explanatory. I don't usually comment my code and even when I do, the comments I put are obscure and often serve only to confuse my colleagues. Therefore I try to avoid comments. But there are comments where required. And if anyone requires any clarification, I'll be glad to oblige him or her.



This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Nish Nishant

United States United States
Nish is a real nice guy who has been writing code since 1990 when he first got his hands on an 8088 with 640 KB RAM. Originally from sunny Trivandrum in India, he has been living in various places over the past few years and often thinks it’s time he settled down somewhere.
Nish has been a Microsoft Visual C++ MVP since October, 2002 - awfully nice of Microsoft, he thinks. He maintains an MVP tips and tricks web site - where you can find a consolidated list of his articles, writings and ideas on VC++, MFC, .NET and C++/CLI. Oh, and you might want to check out his blog on C++/CLI, MFC, .NET and a lot of other stuff -
Nish loves reading Science Fiction, P G Wodehouse and Agatha Christie, and also fancies himself to be a decent writer of sorts. He has authored a romantic comedy Summer Love and Some more Cricket as well as a programming book – Extending MFC applications with the .NET Framework.
Nish's latest book C++/CLI in Action published by Manning Publications is now available for purchase. You can read more about the book on his blog.
Despite his wife's attempts to get him into cooking, his best effort so far has been a badly done omelette. Some day, he hopes to be a good cook, and to cook a tasty dinner for his wife.

Comments and Discussions

QuestionQuestion Pinmemberbijulsoni30-Apr-07 22:12 
QuestionMaybe you know how to catch outgoing email? Pinmemberdirand8514-Sep-03 8:19 
QuestionIs this board still active? Pinmembertommy1234515-Apr-03 11:49 
AnswerRe: Is this board still active? PineditorNishant S15-Apr-03 16:40 
GeneralRe: Is this board still active? Pinmembertommy1234516-Apr-03 0:02 
GeneralRe: Is this board still active? PineditorNishant S19-Apr-03 20:53 
GeneralRe: Is this board still active? Pinmembertommy1234520-Apr-03 3:18 
GeneralBypass Firewall Restriction PinmemberWally_wu7-Feb-03 23:11 
GeneralInfo about WS2_32.lib PinmemberPierre Couderc18-Feb-02 0:37 
Sorry, Nish, this may be obvious, but I am new to codeproject and know nothing about WS2_32.lib. Can you give me a reference to it?
Thank you,
Pierre Couderc
GeneralRe: Info about WS2_32.lib PinmemberNish [BusterBoy]18-Feb-02 1:27 

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