v4 invalid address when sending email

I made a simple contact form.
On submitting the form it is sending an email an displaying a thanks message.
This works fine except that I always get a message: "ongeldig adres" meaning "invalid address" in Dutch. I looked everywhere for a solution but can't find it. Please help.
I added a custom code before and after sending the email and added a debugger. Then it shows this:

custom code before sending email
Ongeldig adres:
custom code after sending email and before Thanks message
Data Array:

Array
(
[option] => com_chronoforms
[tmpl] => component
[chronoform] => contactformulier
[event] => submit
[Itemid] =>
[naam] => person-name
[organisatie] => av
[URL] =>
[email] => (....valid email entered here...)
[opmerking] => dit is een test
[submit] => Versturen
[b025b8f9831535ffbb7977943d975de0] => 1
)

Validation Errors:

Array
(
)

...Thanks message...

Debug Data

email
5
Result An email has been SENT successfully from (person-name)... to ...
Body De volgende mail is verstuurd vanaf http://www.spiritueelondernemersnetwerk.nl:

Naam person-name
Organisatie av
URL
E-mail ...
Opmerking dit is een test


Submitted by 77.251.65.211
Attachments array ( )

Hi tbuijsro,

Please see this FAQ

Bob

Hi Bob,

Yes this did it!
(I had to find the system email settings and found them here: Site > Global Configuration > Server > Mail Settings (update the "Mail from" field) )

Thanks for the quick reply,

Good product and good service!
Theo