From Postmaster Administration Wiki
There is a huge selection of networking tools available to aid with diagnosing & testing, monitoring, and scripting. Here are a handful that are often used with respect to mail:
- dig : A DNS record query tool. Successor to the older host and nslookup tools; the latter is supplied with Windows.
- telnet : The most basic and flexible of tools. While telnet servers have been replaced by more secure ssh servers, telnet client tools remain a popular means of manual testing of text based human readable network protocols, such as SMTP, POP, IMAP, and HTTP to name a few. A telnet client is standard with all operating systems. See Telnet Basics.
- putty : A free, open source ssh and telnet client for Windows.
- kitty : A free, open source ssh and telnet client for Windows based on putty.
- mail : Aka mailx; can be used interactively and scripted to read and/or write mail. While mail tool can be a little cryptic for the average user, it's well worth learning about it as a system administrator since its more often than not that administration is conducted on a console or remote command line shell.
- netcat : Aka nc; a versatile tool for scripting network protocols.
- netstat : Shows active network connections by host and port number. See netstat.
- openssl : A command line interface to a set of tools and functions used to create and manage security certificates.
- ping : Taken from the submariner's sonar term used in echo location, ping simply provides a means to verify if a network-connected host is responsive.
- SSH : Secure Shell; encrypted replacement to telnet; provides additional functionality.
Web Tools & Services
- DNS Stuff : Offers a collection of online tools for DNS and related (regular use requires a subscription). In particular the DNS Report is free and very useful in evaluating the setup of DNS records for a given domain, checking SOA timeout values, MX records, mail server conformance, DNSSEC, and SPF.
- DNS Inspect : Comprehensive validation of a domain's DNS records, like NS and MX setup, NS glue records, web service, etc.
- MX Toolbox: Collection of online tools for DNS, especially aggregated IP and domain blacklist lookups.
- OpenSPF : Explains SPF and provides tools to compose and validate SPF records.
- IPv4 Visual Subnet Calculator : There are many online subnet calculators, but this one is one of the simplest and clearest to use for IPv4. Specify your IPv4 address CIDR mask. Then click divide to split subnets or join to merge a pair back.
- DNS Bajaj : Has one tool to check domain delegations and another tool, DNS Geo, to location TLD name servers.
- Speed Test : One of the more fancy Internet speed test tools, typically used to check ADSL connections.
- Bandwidth Test : Another Internet connectivity test tool.
- DNS Randomness Test : Tests source port randomness of DNS request pertaining to a security issue raised in 2008 by Dan Kaminsky
Security & Encryption Tools
- GnuPG : A complete and free implementation of the OpenPGP standard, as defined by RFC 4880 for encrypted communications. Also supports S/MIME.
- GPGMail : GPG implementation for Mac OS X Mail.
- GPG4Win : GPG implementation for Windows, with the Outlook plugin.
- Enigmail : GPG interface for Mozilla Thunderbird and SeaMonkey.