Direct
Direct email marketing: mailboxes, paper, and one-to-one
Direct mail is paper. Email is digital. 'Direct' also means 1:1 sales mail. Three ideas share a phrase. Keep them straight.

Two industries, one messy phrase
Direct marketing meant measurable, addressable media: catalogs, postcards, telemarketing. Direct mail is the paper half, still run through USPS in the United States and equivalent posts elsewhere. Email inherited the 'direct' label because it is addressable and you can count replies and orders. 'Direct email marketing' in a search bar is often someone mixing those histories, or a vendor selling cold email as if it were a postcard campaign.
Paper and email compete for budget in some retail programs (a catalog plus an email). They do not use the same creative file. A postcard's job is to survive a kitchen counter. An email's job is to survive a preview pane and a spam filter.
Direct mail
Paper, postage, a physical address
A mailbox, authentication, unsubscribe
Direct mail versus email, practically
Direct mail costs per piece (print, postage, list). Email costs per program (ESP, production) with a near-zero marginal stamp. Mail is slower and harder to ignore if it looks like a bill or a real letter. Email is faster and easier to delete. Privacy laws differ: email has CAN-SPAM, GDPR, CASL-type rules; mail has its own list and suppression norms. A 'do not mail' file is not an unsubscribe header.
Use paper when the object matters (a sample, a dimensional mailer, a handwritten note to a small account list). Use email when the news is time-sensitive or the list is large. Using email to mimic a scan of a postcard is usually a worse postcard and a worse email.
'Direct' as in one-to-one
Salespeople say direct email for 1:1 outreach: a message typed (or semi-typed) to one person, often from a corporate mailbox or a sequencer. That is not a newsletter. Deliverability still cares. Fifty 'personal' mails a day from a new domain is bulk in slow motion. Warmup, DNS, and pacing remain email-aisle problems. They are not solved by first-name tokens.
Marketing automation can send 1:1-shaped mail (your trial expired, here is your usage). That is still a template. True 1:1 is when a human would stand behind every sentence. If you cannot, do not pretend. Recipients can tell, and so can filters that look at volume and similarity.
Common questions
Is cold email 'direct marketing'?
In the old catalog sense, addressable commercial mail is direct marketing. In the permission-email sense, cold email is outbound. You can call it direct. Inbox providers will still score it as bulk if you send a lot of it. Plan reputation accordingly, on a domain you can afford to bruise.
Should I run the same offer in a postcard and an email?
The offer can match. The copy should not be identical. Paper needs a physical call to action (a URL short enough to type, a QR if you must). Email needs a button and a preview line. Test them as a pair if you have the budget, not as one asset dumped into two printers.
Related
Prefer markdown? Direct email marketing: mailboxes, paper, and one-to-one.md