Slashdot Mirror
Sendmail Performance Tuning
This book was very easy to read and kept moving along. While I did not find it as much of a page turner as Douglas Adams' Hitchhikers Guide, it did keep me interested. One word of warning though: do not read this when you are tired. You will miss some really good information and have to re-read parts.
I was surprised and very pleased with how much I learned about so many things about Unix, networking and hardware while learning more about sendmail. There is a wide range of information presented that readers at almost any skill level would be able to use. The writing style and use of language was easy to read. The wealth of information packed into the pages of this book I found immediately usable on my Linux boxes and for my job.
I think the only drawback to the book was that there was not more specific sendmail information. Due to the nature of the topic, a lot of the book is devoted to how Unix systems work, more than specific sendmail configuration tasks. Time and detail is spent on other more important considerations such as logging, disk performance, test planning and file systems.
Chapter 1 gets us started with an overview of tuning in general. One of the more important themes of the book is established up front: It is that a cost/benefits analysis should be done for each step.
Sections 1.5, "Tuning Isn't Always Necessary" and 1.6, "Not So Fast ..." establish baseline considerations for making a decision on what, if any, tuning efforts should be made. Throughout the book Christenson reminds the reader to decide on a path that is most cost effective for his organization. Is it the most cost-effective use of the company money and time to have the IT staff hand-craft solutions, or is it better to throw some hardware at the problem?
Let's face it -- if you are running sendmail for a small company and only move a few hundred emails a week, how much performance tuning do you need? If, however, you are running an ISP, a mailing list server or a medium- (or even a large-) sized company mail server, then you need to tune your mail server. This is the book for you. The information in this book, while oriented for sendmail, is actually applicable for tuning any Unix based Mail Transport Agent (MTA) server.
Each solution is an individual matter, that is wholly dependent on several factors. Some of these factors are: volume of email, what the main use of the email system is, how the end users interact with the system, what hardware is being used, how much bandwidth you have and much time and money you have to throw at the problem. Of course, what management considers important is the overriding factor in all decisions.
Chapter 2 is a ten-page introductory overview to sendmail, covering versions, obtaining the (Open Source) code and building sendmail. One of the important things covered is the queue and message spool layouts and permissions. This is helpful for making sense of things later in the book.
A few very important pages are spent on creating the .cf file and why you should use M4, the macro language, for managing the configuration files. Having hand-crafted a .cf file myself several years ago then having to deal with maintaining it, I can vouch for the wisdom of using M4.
The maintainers of sendmail update the M4 macros for new features and changes. The 200 - 300 lines of M4 macro files are converted into a 1500to 2000 line configuration file. While it may be easier to figure out the configuration file to make changes, those changes may not be valid from one version of sendmail to the next.
Christenson admits that he does not always use M4 when in a rush or to test some things. What he does is copy the working configuration file to sendmail.cf.REAL before making changes and updating the .mc file afterward.
The next chapter, Chapter 3 'Tuning Email Relaying' starts with an overview of the email relaying sequence. Most of the discussion in this chapter is not sendmail specific. The importance of data synchronization is emphasized here. Section 6.1 of RFC 2821 is quoted, where it states the email server 'MUST NOT lose the message'. Once that is stated and understood all of the requirements that are discussed in the rest of the chapter are clear.
The next 17 pages are spent discussing how file systems, networking and effective use of file space support, and can detract from, meeting the edict of the RFC. For me, these sections are some of the most interesting, filled with information presented in a concise, readable and detailed manner. I learned a lot about what impact some very basic decisions have on email performance. I also learned how much better I could have made the email servers I have worked on. I will be turning to this chapter the next time I am putting together a box, be it a web server, mail server, file server or even a workstation or laptop. This is a great chapter that can help with any system configuration.
Email reception is covered in chapter 4. Different strategies for verifying recipient, tuning POP and IMAP are covered. Effective use of Local Delivery Agents (LDAs), including procmail, is covered here also.
Additionally, an excellent discussion of storage systems, including disks and solid-state disks, is in this chapter. The sections covering RAID levels, benchmarking and use are well written and informative. Available options on drives, ATA vs. SCSI, Solid State, are just as well done. Section 4.4.2, 'Stupid Disk Drive Tricks,' has some nifty information about how to set up disk drives for even better performance.
Sending email is the next chapter. Here we see some more sendmail-specific information. Tuning of mailing lists and mass mailing is part of the discussion here. One of the more important sections is 'Draining Queues.' How backups are caused and what to do to recover are discussed in this section. This has good information that can be used with any MTA.
One of the most important chapters for me is Chapter 6 'Configuration, Security and Architecture.' Sendmail specific configuration and tuning options are discussed. Section 6.1 covers configuration and is in many ways the heart of the book. This is where sendmail directives that can directly impact performance are covered. How a system's architecture (and DNS) is laid out can have a significant impact on performance.
The section on security is good, but brief. Most of the discussion is on privacy and stopping spam. The use of Transport Layer Security (TLS) is covered in less than a page. With a smattering of security in other parts of the book, this is the sum total of the security discussion of the book. Considering some of the problems with sendmail in the past, I would have liked some more information on this topic.
The next two chapters, 'Finding and Removing Bottlenecks' and 'Load Generation and Testing,' are good, solid, well-written sections that are applicable to most any email system. We are given some effective ways of making systems run better, and how to prove that the system actually does work better. This is where we justify to the boss that the work we have done is really cost effective.
Chapter 9, 'Conclusion' is basically a very brief wrap up and a list of books Christenson thinks we should read.
My own conclusion is that I have learned and relearned a lot of things about Unix and email. Even if you do not use sendmail, I recommend this book without reservation. It is an excellent reference on general system performance tuning, with information on making your sendmail installation run better.
Table of contents
- Introduction
- 1.1 Performance Tuning Examples
- 1.2 sendmail Versions Covered
- 1.3 Definitions
- 1.4 Email Server Tasks
- 1.5 Tuning Isn't Always Necessary
- 1.6 Not So Fast...
- 1.7 Email System Profiling
- 1.8 General Tuning Ideas
- 1.9 Summary
- Sendmail Introduction
- 2.1 Obtaining Sendmail
- 2.2 Building Sendmail
- 2.3 Creating a .cf file
- 2.4 Why Use M4?
- 2.5 System Setup
- 2.6 Summary
- Tuning Email Relaying
- 3.1 What Happens During Relaying
- 3.2 Synchronization
- 3.3 File Systems
- 3.4 File Space
- 3.5 Networking
- 3.6 Summary
- Tuning Email Reception
- 4.1 What Happens During Email Reception
- 4.2 Recipient Verification
- 4.3 Storage Systems
- 4.4 Disks
- 4.5 Solid State Disks
- 4.6 POP Tuning Specifics
- 4.7 Message Storage Hashing
- 4.8 IMAP Tuning Specifics
- 4.9 Summary
- Tuning Email Sending
- 5.1 Mailing Lists
- 5.2 Command-Line Message Generation
- 5.3 Draining Queues
- 5.4 Another Mailing List Strategy
- 5.5 SMTP PIPELINING
- 5.6 More Notes on Mass Mailing
- 5.7 Summary
- Configuration, Security and Architecture
- 6.1 Configuration
- 6.2 Security and Performance
- 6.3 Other General Strategies
- 6.4 Summary
- Finding and Removing Bottlenecks
- 7.1 Kernel Parameters Run Amok
- 7.2 The Quick Fix
- 7.3 Tools
- 7.4 syslog
- 7.5 Removing Bottlenecks
- 7.6 Summary
- Load Generation and Testing
- 8.1 Test System Setup
- 8.2 Testing Tools
- 8.3 Load Testing Pitfalls
- 8.4 Summary
- Conclusion
You can purchase Sendmail Performance Tuning from bn.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.
Since Sendmail hasn't been monolithic for a couple of versions now, have you considered switching back?
Dewey, what part of this looks like authorities should be involved?
The thing that Sendmail did well, address rewriting, is irrelevant for today's net, and can be done more readably in many other ways. Even a Perl script is much more readable :-) Installing one as a Postfix transport is trivial.
I'm surprised that there isn't more business action around Postfix.
Bruce
Bruce Perens.
My former employer, AT&T Canada, who has over 150,000 home users and several thousand business
clients, dumped their Sendmail-on-Solaris servers in favor of Postfix-on-FreeBSD and have never been happier.
Pain is merely failure leaving the body
Sendmail's default configuration is very conservative with respect to both your machine resources, and the resources of those with whom you exchange mail.
Run sendmail with
(or something bigger, if you want) and you can get past the biggest hurdle in sendmail performance -- by default, sendmail will handle all outgoing messages in a single queue. (Both qmail and postfix use multiple queues and/or runners by default.)Sendmail can relay messages without doing any disk I/O, thanks to the asynchronous I/O libraries; coupled with multiple queue runners, it's hard to get faster performance out of any MTA.
You (and the others following this thread) owe it to yourselves to give postfix a try. It is clean, and elegant. All of it's configs live in 2 files (main.cf and master.cf), and it is powerful.
Postfix has solid anti-spam measures, fantastic performance, readable config files (that are well commented from the start... heck there are about 10-20 comment lines per config line), and you only need to set like 3 lines in the config to get a working mail server.
Zapman
These days, Red Hat's default install of sendmail does not accept remote connections. Red Hat tells you to use M4 to generate a new CF file to enable this functionality.
Here is what you really do...
Find the line in the CF file that reads:
O DaemonPortOptions=Name=MTA
and change it to:
O DaemonPortOptions=Port=smtp,Addr=0.0.0.0, Name=MTA
I picked this up from a bugzilla comment.
postfix exploit
Found this by typing, "postfix local exploit" on google. Seems there were tons of other hits on this too (about 6,900).
You can run dictionary attacks against domains I handle mail for, but at least it will take you a damn long time! I just wish everybody was doing it. Eventually it would take too long to spam effectively.
...to repeat it.
Um, wait. That didn't come out right.
Sendmail is so bloated that it apparently takes books to get decent performance out of it.
Seriously, a lot of people just don't understand sendmail and how difficult mail routing is. Sendmail is bloated because it tries to solve a very complex problem in an extremely diverse environment.
Postfix was so easy to use, that I went from reading the man pages to a working system in one hour.
Postfix and sendmail are going in two different directions. Sendmail == configurability, postfix == ease of use.
Sendmail is fast. Not because there's a book on performance tuning does it mean the software is slow. Sendmail is probably as fast as anything else out there.
Sendmail is configurable to no end. I run a sendmail setup with virtual domains, lots of address rewrite rules, spam filters. All my virtual users, and alias maps are in LDAP. I modify all my sendmail virtual users, virtual domains, aliases, etc through a PHP website. Try that with other mailers. They support LDAP, but they are no where as configurable as sendmail.
Then try running these mailers on Linux, bsd, solaris, windows, AIX, etc., etc. No OS lock-in.
Sendmail is well documented.
The prevaling mood on /. these days seems to be if it's not brand new, get rid of it. That's unfortunate.
Based on upvotes, Ageism is the only "-ism" Slashdotters care about and think isn't SJW
The hole -- which was very, very small to begin
with -- has been closed. Please stop spreading
misinformation.
Ben "You have your mind on computers, it seems."
Wrongo here!
I know both qmail and sendmail. With sendmail I can do almost everything I need. With qmail I have to search Internet for bits of information, patches and them write my own patches because of simple-minded approach of qmail author. A lot of corners were cut to make qmail faster - it made it very inconvenient to have it in production environment.
Qmail just lacks flexibility...