MailFlow
MailFlow is a plugin for Apple Mail on OS X 10.12 and later, fixing it to emit RFC2646 format=flowed plain text messages and taming its enthusiasm for quoted-printable transfer encoding. Quoting and attribution when replying is also improved, and a long-standing bug in the display of plain text messages is fixed.
Mail was once quite a good 'net citizen. It could be configured to generate plain text email, and would do so with the text neatly wrapped at 76 columns. In addition, it used the RFC2646 format=flowed extension to indicate that these wrapped paragraphs could be reflowed. Thus mailing list archives and traditional mail clients saw readable 80-column text without noisy encoding, but more sophisticated readers could re-fill the paragraphs to suit the display width.
Unfortunately, Mail is poorly maintained and has declined in quality over recent years, with many bugs introduced and incompetent design choices made. Current releases have ditched format=flowed for plain text parts, instead opting to emit each paragraph as a single long line. If this is longer than 77 characters, the text is mangled with a quoted-printable transfer encoding. The resulting email leaves a very visible mess in mailing list archives on the web, as well as drawing understandable ire from recipients with traditional unix mail clients.
Fortunately, even if Mac users find themselves attracted to Apple Mail for its convenient reading interface and good platform integration, all is not lost. Mail has been furnished with a plugin interface, albeit an undocumented one, and MailFlow hooks into this to improve the situation.
Installation
MailFlow is currently compatible with Apple Mail 10.0 and later. To install, unpack the source tar.gz file, change to the unpacked directory and run
/usr/bin/python install.py
Plugin bundles contain a list of UUIDs identifying versions of Mail with which they are compatible. The install.py script extracts the correct UUID from the installed version of Mail, generates a MailFlow.bundle to match, and installs it in ~/Library/Mail/Bundles/. You will need to quit and relaunch Mail for the plugin to be registered.
Sometimes when Mail is updated, its compatibility UUID changes. Mail will then disable plugins, moving them from 'Bundles/' to 'Bundles (Disabled)/'. The user is notified when this happens, and it is sufficient to simply run the install.py script again. The old disabled bundle will be cleared away, and a new one built and installed to match the new version of Mail.
Features
Most of MailFlow's functionality should be transparent to a Mail user unless the raw source of sent messages is examined. Its primary feature is to break paragraphs into reflowable lines in RFC2646 format=flowed format and disable quoted-printable transfer encoding for plain text email.
In outbound plain text messages, lines are broken at word boundaries to wrap the text to 76 columns wide, and a trailing space is added wherever a line has been broken. Where a line to be broken is quoted, the continuation line is quoted to the same level. Finally, to signal the message has been flowed, the parameters format=flowed and delsp=yes are added to the text/plain content-type. The result is a visually clean plain text message, correctly wrapped for 80 column displays, but clients aware of the format=flowed extension can spot the trailing spaces, reassemble paragraphs and reflow them to fit displays of differing widths. This is especially useful for mobile devices.
Unlike Apple's original format=flowed implementation, MailFlow will never break a line within a word, even if that word is longer than 76 characters. This was typically an issue with long URLs pasted into messages: breaking these to fit an 80-column display usually causes more problems than it solves, and some format=flowed aware clients do not fully support the delsp=yes modifier needed to reassemble them. However, as with Apple's original implementation, MailFlow implements space stuffing for unquoted lines beginning with ' ' or 'From '.
Lines indented with whitespace are not flowed, whether or not they are quoted, and any trailing whitespace is removed to avoid clients from trying to reflow them. This provides a convenient way to include non-reflowable content such as quotes, code samples, aligned columns or ASCII art whilst composing a plain text message.
For convenience when indenting text blocks, the built-in Increase/Decrease Indentation operations are extended to work on plain text messages. These will insert or remove two spaces at the start of the current line or all lines overlapping the current selection.
Flowed format is not appropriate for some messages, such as those containing inline patches. To disable the use of flowed text for an individual message, hold down the Option key when clicking on the Send button in the toolbar, or when selecting Send from the Message menu. MailFlow will still restrict unnecessary use of quoted-printable even when format=flowed is disabled.
By default, Mail uses a quoted-printable transfer encoding for text/plain parts whenever they contain non-ASCII characters or a line longer than 77 characters. MailFlow relaxes this behaviour for text/plain, using a 7-bit transfer encoding for plain ASCII and an 8-bit transfer encoding otherwise, provided the lines do not exceed the 998 column limit imposed by SMTP. Note the outbound mail server must support the 8BITMIME ESMTP extension (RFC1653/RFC6152) but all modern SMTP servers are fine with this.
MailFlow will trim the excessively verbose attribution line Mail inserts when composing a reply, i.e.
On 8 Apr 2014, at 10:08:34, Chris Webb chris@arachsys.com wrote:
becomes
Chris Webb chris@arachsys.com wrote:
Since version 8.0, Mail has a bug which causes the attribution line to be quoted as if it were part of the original message. MailFlow will also fix this whilst trimming the attribution line.
MailFlow makes it easier to forward messages as proper MIME attachments instead of quoting them inline. Mail has always supported MIME forward but relegated it to the Message menu without a shortcut or toolbar button, instead encouraging ugly inline forward. MailFlow reconfigures the standard forward buttons, keyboard shortcut and menu item to use MIME.
To override this and forward a message inline, hold down the Option key when clicking on the Forward button in the toolbar or when selecting Forward from the Message menu.
Finally, MailFlow addresses a very long-standing bug in Mail, which drops
one leading space from every indented line of a plain text message in the
message viewer. When converting the text/plain part to HTML for display in a
WebView, all but the first leading space is rendered as ' ' so, for
example, a line ' foo' becomes '
foo'. However, WebKit will then
display this as ' foo' not ' foo'.
To work around this bug, MailFlow translates a space following a '
' (or
at the start of the message) into ' ' before a plain text part is
rendered in a WebView.
pbmbox
For command-line users, the MailFlow distribution also includes a small utility, pbmbox. When messages are selected and copied in Mail, they are added to the clipboard as RFC822MessageDatasPboardType objects. pbmbox decodes these objects and emits the messages in unix mbox format on stdout.
To install, copy it to a directory in your PATH and make it executable:
sudo install -m 0755 pbmbox.py /usr/local/bin/pbmbox
A typical use is importing a patch series from email into a git repository. Select the messages in Mail, copy them with Command-C, and then run
pbmbox | git am
within the repository.
By default, the mboxrd format is used: lines beginning with />*From / are quoted with one additional leading '>'. This encoding avoids corruption of messages and is always reversible. If the -n or --no-quote-from option is given, pbmbox will not attempt to quote 'From ' lines. This is sometimes useful for simple command-line handling of a single message, where no ambiguity can result from an unquoted 'From '.
Copying
This software was written by Chris Webb chris@arachsys.com and is distributed as Free Software under the terms of the MIT license in COPYING.