The man page says the default value for the syntax option is off, but I get syntax highlighting anyway because of the filetype plugin, which is enabled by default (at least on OpenBSD current).

It would be better for the man page to describe what actually happens.

(Would it be better to make the default be called auto, and make off signal to the filetype plugin that it should leave the option alone? I'm new to vis, but as an initial impression, needing to subscribe to WIN_OPEN to disable syntax highlighting seems a bit messy.)

https://lists.sr.ht/~rjarry/aerc-devel/patches/33568 addresses this.

I decided to make it a configuration option instead of the suggested -u flag because the :view command isn't the only thing that can cause a message to get viewed. I changed NewMessageStoreView so that a new configuration option controls whether it marks the message as seen.

I use the "seen" flag to mark messages as "dealt with", and don't want messages to be automatically marked as seen.

I brought this up on IRC last month and ~rjarry suggested adding a -u flag to :view which prevents it from marking the message as read.