The Mac has a genuinely good native answer for single emails and needs a small step up for bulk, so both halves:

Single email, native and clean: in Apple Mail select the message, File, Print and in the print dialog use the PDF dropdown at the bottom left, Save as PDF. The Mac's system wide PDF engine renders the email, headers and body, into a clean PDF, no software needed. This is the Mac doing what it does well, print to PDF built into the OS and it produces a proper records quality PDF every time.

The Export as PDF alternative: Apple Mail also offers File, Export as PDF in recent versions, a direct route to the same result without the print dialog, worth knowing as the even shorter path where your Mail version has it.

Bulk, where native stops: selecting multiple messages and printing does not cleanly batch them into separate PDFs, so bulk needs either a repeated single operation for a handful, tedious past a few or an Automator workflow that iterates selected messages saving each as PDF, the Mac's built in automation doing the batch the print dialog will not. Automator's Mail actions plus a save as PDF step build a reusable droplet for recurring batch needs.

The attachment caveat, same on every platform: printing captures the message body and attachment names, not attachment contents, which save separately from the message. For records where attachments matter, save the email PDF and its attachments together into a per matter folder, the pairing that keeps the record complete, since the PDF alone documents the message but not what came with it.