PHPMailer：在HTML电子邮件中插入签名块

I've been using PHPMailer without too many issues, but the last request I received had me spending hours without a solution. No one else seems to have had that issue and not a single example can be found online.

We generate the HTML email in real time because it has to be populated by some calculated field, so no import from a file. I've been asked to insert an ordinary signature with the usual standard prefix "-- ". The problem is: no matter what I try, no email client recognizes the signature block.

I'm aware that it usually is just an ordinary dash dash space . No rocket science here. Yet...

Some solution I tried, sparsed:

    $body .= "-- ";
    $body .= "-- <br>";
    $body .= "-- " . PHP_EOL;
    $body .= "<p>-- </p>";
    $body .= "-- 
";
    $body .= "-- 
<br>";
    $body .= "-- 
" . PHP_EOL;
    $body .= "<p>-- 
</p>";
    $body .= "--&nbsp;
";
    $body .= "--&nbsp;
<br>";
    $body .= "--&nbsp;
" . PHP_EOL;
    $body .= "<p>--&nbsp;
</p>";
    $body .= "--  
";
    $body .= "--  
<br>";
    $body .= "--  
" . PHP_EOL;
    $body .= "<p>-- 
</p>";
    $body .= "-- 
";
    $body .= "-- 
<br>";
    $body .= "-- 
" . PHP_EOL;
    $body .= "<p>-- 
</p>";
    $body .= "--  
";
    $body .= "--  
<br>";
    $body .= "--  
" . PHP_EOL;
    $body .= "<p>--  
</p>";

And many more. Like 200 more.

Probably the answer is a simple thing that I missed, but I'm completely lost right now.

[ Sorry for my english ]

[EDIT]

1) What I expect from the client when it encounters the block -> that it recognizes it as a signature. That means that Gmail will put "..." while Thunderbird (in my case and with my settings) would plain cut it in the reply.

Before: https://i.stack.imgur.com/2YaCK.png After: https://i.stack.imgur.com/haWIi.png

2) Which clients did you check? -> Gmail and TB.

3) Manual check -> Yes of course. My email has one and I'm 100% certain that it works.

What I noticed in Gmail is that, in "Show original", an ordinary mail is like this one:

    *aaa*

    *dsadfv*
    vsdfv <http://www.google.com>
    fdvsdfv
    -- 
    dsfgsdfv

While mine is always a variation of this one:

    <br>-- =20

What I mean is that not a single line begins with the double dash but is always preceded but the previous line separator, plus it ends with =20 that Gmail uses as a return.