Solo Mailing

Solo mailing
A one-time broadcast to an email list, separate from regular newsletters or promotions, and often including a message from an outside advertiser or a special promotion from the list owner.
SPAM ...

solo mailing
a database innovation in which a customised marketing piece is prepared to appeal to one individual's interests
solution selling ...

Many email clients permit you to send a test email before sending a regular email newsletter or solo mailing, ...