When comparing st vs Postbox, the Slant community recommends Postbox for most people. In the question“What is the best desktop Email client for Windows 10?” Postbox is ranked 5th while st is ranked 7th.
Ranked in these QuestionsQuestion Ranking
Pro Low memory usage
st is built to serve as a lightweight terminal emulator. It's very light and doesn't require many resources to run, making it able to run well on older and low-end machines.
Pro Extremely simple architecture
st consists of a single C file that takes seconds to recompile. This also makes it very easy to understand and customize.
Pro 24-bit "True Color" support
st supports color escape sequences for a full 16 million 24-bit color spectrum, instead of the typical 256 colors.
Pro Support for fontconfig
There is full XFT (X Free Type interface library) and fallback font support through fontconfig in st. If your selected font is missing a certain glyph or symbol, but one of your other installed fonts has it, it will be shown.
Pro Copyfree licensing
Copyfree licensing implies that the user has the freedom to copy, use, modify, and distribute what he/she possesses.
Pro Image previews
Handles image previews (e.g. in ranger) way better than other terminal emulators.
Pro Patches are great
The patches on the site are great. Scroll back, hide the mouse, etc.
Hackable and lightweight.
Pro Blazing fast
it is extremely responsive and fast, even on older computers.
The terminal doesn't have any bloated features nobody uses. It is very minimal and extendable.
Pro Clear interface
Pro Forgotten attachment reminders by default
Reminding the user that they forgot to attach the file if they mentioned one in the body of the email is one of the most useful features of any email client and so many don't include this. Postbox is pre-configured to look for certain keywords (attached, CV, spreadsheet, pdf etc) and you can specify your own keywords in addition.
Pro Blocks tracking gifs
Has the ability to block tracking gifs commonly used for read receipts.
Pro One Inbox for all accounts
All messages in one place. But you can select to show only messages from each account either.
Pro Quick Bar for macros
Quick bar allows you to add a variety of content to your message. It will let you reuse URLS in your Sent folder, and autocompletes against canned responses, signatures, and topics.
Con Configuration requires recompiling
Though recompilation takes seconds, knowledge of C header files is required for customization (though it's pretty easy to do for someone who knows how to edit config files).
Con Text is cut off when resizing windows
In the vanilla build, when reducing windows, lines do not wrap, they are cut off. When the window is made large again, some of the text is missing.
Con Crashes when some characters or colored fonts are displayed
Con No scrollback by default
The best way to perform scrollback is to use a multiplexer (such as tmux, screen, or dvtm) if you want scrollback and reverse-search support.
Con New features means installing patches
Just to get copy/paste support and scrolling, you have to install patches. And it's not that intuitive for a beginner.
Con Internal border/margins
Doesn't support internal margins.
Con Source code edits (aka configs) need to be redone after updating
Con Imperfect fontconfig support for CJK characters
It [st] doesn't seem to use CJK fonts provided by fontconfig while other programs use such fonts.
Con No support forum
Support for paid product has no online forums.