As one of many ex-Evernote users that’s bounced around the notes apps world chasing shiny things, (I settled on Obsidian), I haven’t found a good way of handling emails which are about 50% of my reference information with bills, documents and other detritus of life.
At the moment I drag each individual file to finder folders and let Obsidian look at it, but it’s clunky and opens a new app etc.
How are you handling emails in your notes / PKM system?
Short answer: I file them in DEVONthink. I can organize them there by topic, project, date/time, etc. Obsidian is great at what it does, but I keep all of my “bills, documents and other detritus of life” in DEVONthink.
(I also like that the link to the original email in Apple Mail ‘sticks’ to the .eml file in DEVONthink, so if I double-click it, it quickly opens up again in Apple Mail, even if it’s an email from years ago.)
I usually just hit the F1 hot key and a selected e-mail is copied into my EagleFiler app.
At the end of the year, I export all archived e-mail from Apple Mail as an .mbox file, which I save. Then I import that file into an EagleFiler library dedicated to e-mail, which allows me to search and view my old e-mails. Also speeds up Apple Mail. 
This is what I do, too. I import all of my administration-related documents into the appropriate DTP database along with any relevant email. Once the email is in DTP, I delete it in my email client.
I often use Hookmark (formerly Hook) to hook an email to the relevant note in Obsidian. I’m most likely to paste the markdown link into the Obsidian note, but sometimes I do the “Hook to Copied Link” thing, too.
It works really well. I can easily get back to the relevant email from the Obsidian note.
I’ve been leaving all my email on the server for the past twenty years or so. I was a long time Evernote user and it took me a while before I found a permanent replacement, but I finally settled on Google Workspace. Some of my files are linked together, or to calendar events, etc. and I routinely link emails and tasks. But most of the pdfs, text files, docs, and spreadsheets are just stored on Google Drive. The Cloud Search feature, available with a business standard account, will search email, contacts, calendar, files, tasks, contacts, etc. with a single query. It’s all I need.
And much like @karlnyhus I use EagleFiler to backup my email. I schedule a once a month download of all my data in my GW account and import the .mbox file into EF.
I’ll forward my email to Mail Drop To Drafts. From there I summarize what I need, remove the excess, and have an action that sends it to obsidian.
I use DevonThink and NotePlan - once the email is in DevonThink, I copy a link to the item and paste it into NotePlan. That works across all my devices (iOS, iPadOS and MacOS).
I use Mailmate to Devonthink. It works perfectly. It saves perfect email text and attachments while providing a link if I want to the original email.