mails wrongly cut (in 72 chars) causing trouble with links

Silverstripe Version:
4.9
Question:
Sometimes links are corrupted in mails I generate using templates causing images of sponsors not displaying.

I generate mails using templates. Sometimes images are not displayed in the mail because the link is corrupted. I can see that in the raw source that the link has been cut after a dot. See hereafter (the first image displays correctly, the second does not).

<img=20

src=3D"http://w=

ww.porschefriends.eu/public//assets/U/SP/Marcolini.png"

style=3D"max-wid=

th:250px; width:100%;" class=3D"center"/>

<img=20

src=3D"http://www=

…porschefriends.eu/public//assets/U/SP/Cuberdons-LEOPOLD.jpg"

style=3D"m=

ax-width:250px; width:100%;" class=3D"center"/>

There must be a bug and I would like to correct the issue. Where in Silverstripe are the mails cut? In which php file?

Thanks for your help
Philippe