Interesting observation, but it appears that passing a string returns the same output as passing an array ref. Passing a string as the value of the paramater is even used in the source of the MIME::Entity module itself for its own internal methods (see, add_sig() ).

The docs actually state the value for the Data param should be,

Single-part entities only. Optional. An alternative to Path (q.v.): the actual data, either as a scalar or an array reference (whose elements are joined together to make the actual scalar).

So both are right. I'm very pleased with how MIME::Entity is encoding the message - one line that I feed it splitting into two lines when encoded is what I expect. Decoding things back works just as well. (I'm not reporting a bug in MIME::Entity.)

 
#!/usr/bin/perl 

use MIME::Entity; 

my $str = 'filler text to get the first char of line 2 to be a dot______ http://google.com'; 

MIME::Entity->build(
	Data     => $str, 
	Type     => 'text/plain',
	Encoding => 'quoted-printable',
)->bodyhandle->print; 

filler text to get the first char of line 2 to be a dot______ http://google.com

The broken URL isn't happening in my app, but upstream.

The problem is in the SMTP client not double-dotting a line that starts with a dot. Lines that start with a dot could happen because of my example (wrapping a URL onto multiple lines during encode). I'm asking what it is I should do (if anything) to deal with a broken SMTP client? I'm leaning on, "nothing", but is this instead a universal problem, with a known solution? Googling this problem specifically for Perl examples leads to no results, although other languages/libraries say to encode the dot. If I were to encode the dot, what's the least hackiest way to do so? I can make a one-line regex to handle this, but then I fear I'll then have two problems.