The phrase "a single mail" is correct and usable in written English.
It can be used when referring to one piece of mail or one email in a context where you want to emphasize the singularity of the item.
Example: "I received a single mail today, and it contained important information regarding the project."
Alternatives: "one email" or "a solitary piece of mail".
Across the Hudson, at the Valley Animal Hospital in Clifton, N.J., there are seven clients who go by the name Jeter, and on a single mail route in nearby Montclair, there are at least two Jeters — both reported to be friendly.
A single mail order can take minutes to process, while a web order using authentication like Ticketmaster's Verified Fan takes milliseconds.
If they prefer, authors may go to their MySpringer account and opt to receive weekly, monthly or annual alerts listing all citations in a single mail.
If they prefer, authors may go to their My Springer account and opt to receive weekly, monthly or annual alerts listing all citations in a single mail.
Conversely, lists should not be used for formatting non-list content such as a single mailing address.
We have just had a record take-up from a single mailing with Louisville Water Company in Kentucky.
I write a daily journal of my activities, which is combined at the end of the week into a single mailing to my children.
And he even criticised the Labour party, saying that it was "absurd" that all the deputy leadership candidates had to send their literature to party members separately when it would have been far cheaper to include all leaflets in a single mailing.
We distributed a total of 1,000 questionnaires in a single mailing by US Postal Service.
If the company fills its inventory and puts two ads in Jesse Berst's "Anchordesk" update, a single mailing would rake in $120,000.
Combining market research and fundraising into a single mailing is an ethically questionable practice that violates the trust of the participants.
