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Thunderbird/Seamonkey Tricks

A lot of people do not know there is a dedicated desktop application for email. Hence, this article.

In 2004, Google introduced the Gmail service with a 1 GB mailbox and free POP access. That was a time when most people had email accounts with their ISP or had free webmail accounts with Hotmail or Yahoo. Mailbox storage was limited to measly amounts such as 5 or 10 MB. If you did not regularly purge old messages, then new incoming mail would get bounced. People who tried to contact you would get the dreaded "inbox full" error. Hence, it was a standard practice to store email "offline" using an email client. Each year now, a new generation of young people (mostly students) discover the Internet and they start with webmail straightaway. As popular webmail services integrate online chatting as well, they prefer to use a web browser rather than a desktop mail client to access email. This is sad because desktop email clients represent one of those rare Internet technologies that can claim to have achieved perfection. This article will bring these people "up to speed" on Thunderbird, the most popular FOSS email client.

Why use a desktop email client

With an email client, you store email offline, that is, on your hard disk. After the email application connects to your mail server and downloads new mail, it tells the server to delete those messages from your mailbox (unless configured otherwise). This has several advantages.

Gmail inbox screenshot

Live off the grid with no mail online. To get this Gmail note, you will have to empty the inbox and trash, and also delete all archived messages.

POP or IMAP access to email

Email clients access mail using two protocols, POP and IMAP, to receive mail. POP is best if you would like to download and delete mail. IMAP is best if you need access on multiple devices or at different locations. POP is more prevalent than IMAP. For offline storage, POP is the best. Popular webmail providers provide both POP and IMAP access. Before you can use an email client, you will have to login to your webmail provider in a browser, check the settings and activate POP/IMAP access for incoming mail. Email clients use SMTP protocol for outgoing mail. In Thunderbird/Seamonkey, you may have to add SMTP server settings separately for each email account.

If you have lots of email already online, then it may not be possible to make your email client create an offline copy in one go. Each time you choose to receive messages, the mail client will download a few hundred of your old messages. After it has downloaded all your old archived messages, the mail client will then settle down to downloading only your newest messages.

The settings for some popular Webmail services are as follows:

The following settings are common for them:

Some ISPs and hosting providers provide unencrypted mail access. Here, the connection security method will have to be "None", and the ports are set to 110 for POP and 25 for SMTP. However, please be aware that most ISPs block port 25 and many mail servers block mail originating from that port.

Thunderbird and Seamonkey

Popular email clients today are Microsoft Outlook and Mozilla Thunderbird. Thunderbird is the obvious FOSS option. Like the browser Firefox, Thunderbird is a modern software and supports many extensions or add-ons. Unlike Outlook (which uses Microsoft Word as the HTML formatting engine), Thunderbird has better CSS support as it renders HTML messages using the Gecko engine (like the Firefox browser).

The Seamonkey internet suite bundles both the Firefox browser and Thunderbird mail clients, in addition to an IRC client and a web page designer. Seamonkey is based on the philosophy of the old NetScape Internet Communication Suite, in which the browser was known as Netscape Navigator and the mail client was known as Netscape Communicator. Because of certain trademark objections with Mozilla, some GNU/Linux distributions bundle Firefox and Thunderbird as IceWeasel and IceDove. Seamonkey became IceApe. This was resolved in 2016.

If you have already opened the Seamonkey browser, then the Seamonkey mail client can opened in a flash. The vice versa is also true. This is very useful because website links in the Seamonkey mail are opened in Seamonkey browser. Firefox is a separate application from Thunderbird and does not have the same advantage. For this reason, I use Seamonkey instead of Thunderbird. Seamonkey is available at

By default, Seamonkey looks like Firefox or Thunderbird. I prefer to change its appearance using the Modern theme, as it makes it look like the old Netscape 6 and also because I need the browser to look different from regular Firefox. To enable this theme, choose from the menu Tools » Add-Ons » Appearance » Seamonkey Modern.

Even on a desktop screen, space may be at a premium. Currently, Thunderbird/Seamonkey does not provide an easy way to customize the date columns. I use this trick in the launcher command to fix it.

export LC_TIME=en_DK.UTF-8 && seamonkey -mail

Columns in Thunderbird inbox

Changing format of the date columns requires a hack.

Email filtering

Email providers today do a good job of filtering junk mail. You can still do a better job with your own mail filters (Tools » Message Filters). You can choose to move/delete messages based on the occurrences of certain words in the From, To or Subject headers of the email.

Mail filters in Thunderbird

Configure your own mail filters.

Email spoofing

Whether you use webmail or a desktop client like Seamonkey, you need beware of email spoofing. Email service providers usually do a good job filtering out such messages but not always. Some fake email does come through. You can look at the headers in the email and verify if the email is coming from a legitimate mail server. Specifically check the SPF (Sender Policy Framework) header. There are other verification headers such as DKIM and DMARC but not all mail servers have them. SPF is the minimum you should check, particularly when dealing with someone new.

In Seamonkey, you can select an email and click on View » Message source to view all the headers in an email.

Email header

When a new Internet domain is registered and configured, the owner will specify which mail servers are authorized to send email on its behalf. (The mailserver and the webserver can be different.) Any mail that does not pass the SPF test should be considered suspicious. Your email provider will do the SPF test and add a header for it in the email.

There are several headers in an email. SPF header is the one you should check. You can also check the Received headers. There will be several of them but the one of them will tell you the IP address from which the email originated. You can do a reverse lookup on this IP and find out which ISP the sender had been using. You might also be able to get the rough location of the person by doing a geolocation test on the IP. If you get a mail from Harvard and the geolocation reveals that it is from India or Israel, you know it is a spoofed email.

Sometimes, the SPF record will indicate that it is clean but the domain itself may be fake. In 2020, several journalists were sent fake emails offering jobs at Harvard University. The scammers had registered domain Verifying the SPF record would have been fruitless because the university real domain is at

Even with these preliminary checks, there are ways that scammers can get through. It takes years of experience for a mailserver administrator to correctly verify emails. It is a constantly developing art form. So, it is best to treat all unsolicited mail with suspicion. Do not click any links in the email. Go directly to the website (by manually typing the address in the browser) and check if the sender is a real person and is listed on the site.

Thunderbird as an RSS reader

Apart from email, Thunderbird can also display content from RSS feeds. It stores articles in the RSS feed offline, just like email messages.

Thunderbirds as an RSS feed reader

Thunderbird is also an RSS feed reader. (Does Twitter provide RSS feeds? It used to but not anymore. I use my TweetsToRSS app for that. Subhash TweetsToRSS is a readonly Twitter server, not client)

Thunderbird as an NNTP client

Usenet newsgroups predate the World Wide Web. They are like an online discussion forum organized into several hierarchical groups. Forum participants post messages in the form of an email addressed to a newsgroup (say comp.lang.javascript) and the NNTP client would thread the discussions based on the subject line. (Google Groups is a web-based interface into the world of Usenet.)

A newsgroup user sends an email message and the NNTP server converts it to a forum post. Now World Wide Web access is required.

Seamonkey ChatZilla

Apart from the Firefox-based browser and the Thunderbird-based email client, Seamonkey also bundles an IRC chat client. IRC is yet another Internet-based communication protocol that does not use the World Wide Web. It is the preferred medium of communication for hackers (not the bad kind). Here is a link for starters: irc:// Many IRC servers are accessible only via a special port, usually from 6660 to 6669. Check with the server and unblock this port in your network's firewall/modem/router.


When you store email offline, the burden of doing regular backups falls on you. You also need to ensure that your computer is not vulnerable to malware such as email viruses. Webmail providers do a good job of eliminating email-borne malware but malware can still arrive from other sources. Windows computers are particularly vulnerable to malware spread by USB drives and browser toolbars and extensions. (In Windows, simply creating a directory named "autorun.inf" at the root level stops most USB drive infections.) Seamonkey stores all its data (email messages and accounts, RSS feeds, website username/passwords/preferences, etc.,) in the ~/.mozilla/Seamonkey directory. For backup, just zip this directory regularly. If you move to a new GNU/Linux system, restore the backed-up directory to your new ~/.mozilla directory.