How to forward all Slack messages to an email address, or a folder on disk?

It seems the higher-ups are gonna force us to use Slack instead of Jabber/email which we've used successfully for years. I'm not very happy about this, since it seems like a captive closed platform where all data is hosted by Slack, no integrity of data and access is guaranteed , and I won't have the messages in readable format on my computer for grepping.

So if I'm gonna use it, I'd like to have all Slack communication archived on my machine or in my mailbox independently of Slack. This will be useful e.g. in case I need to access past messages as they were (in case I can't access them on Slack due to outage, or someone tampering with them). It seems in past one could use Pidgin to use Slack, and maybe also set up local archiving, does anybody still use this?

How do you use Slack securely on your machine? Do you use some forwarding to e-mail or to disk?