...you put a backslash before the '@' character(s) in your string literal(s) :)

Background is that when Perl sees something like "foo abc@xyz bar", it attempts to interpolate an array @xyz, and if there is no such array in the program, Perl warns that this interpolation might be unintended...

BTW, with use diagnostics, you would have gotten virtually the same explanation for free:

Possible unintended interpolation of @xyz in string at ...
    (W ambiguous) You said something like `@foo' in a double-quoted st
+ring
    but there was no array @foo in scope at the time. If you wanted a
    literal @foo, then write it as \@foo; otherwise find out what happ
+ened
    to the array you apparently lost track of.
[download]

You've received essentially this answer to each question you've posted. Please help us avoid the waste of storage and bandwidth by including code and data (if relevant) each time you post a new question.

Possible unintended interpolation of %s in string

(W ambiguous) You said something like `@foo' in a double-quoted string but there was no array @foo in scope at the time. If you wanted a literal @foo, then write it as \@foo; otherwise find out what happened to the array you apparently lost track of.

@ now always interpolates an array in double-quotish strings.

print "To: someone@somewhere.com\n";

# perl4 prints: To:someone@somewhere.com
# perl < 5.6.1, error : In string, @somewhere now must be written as \
+@somewhere
# perl >= 5.6.1, warning : Possible unintended interpolation of @somew
+here in string
[download]