Form EmailFinisher with SmtpTransport

Hi, I have problems sending a form via smtp:
It’s a Neos form with an email finisher. I extended the contact example.
When I put the form inside a page for the first time, I got the Exeption:

The Preset "bootstrap" was not found underneath TYPO3: Form: presets.

page<TYPO3.Neos:Page>/ body<TYPO3.TypoScript:Template>/ main<TYPO3.Neos:ContentCollection>/ content<TYPO3.Neos:ContentCollectionRenderer>/ itemRenderer<TYPO3.Neos:ContentCase>/ default<TYPO3.TypoScript:Matcher>/ element<TYPO3.Neos.NodeTypes:TwoColumn>/ columns<TYPO3.TypoScript:Collection>/ itemRenderer<TYPO3.Neos.NodeTypes:MultiColumnItem>/ content<TYPO3.Neos:ContentCollectionRenderer>/ itemRenderer<TYPO3.Neos:ContentCase>/ default<TYPO3.TypoScript:Matcher>/ element<TYPO3.Neos.NodeTypes:Form><TYPO3.Neos.NodeTypes:Form>/

In the settings.yaml of the form package there was no bootstap preset, but a default preset.
I changed the name to bootstrap and got rid of the exeption.
Everything seems to be ok.
I installed SwiftMailer with composer.
The email finisher with the mBoxTransport just works fine.
Sentmail is not available nor recomended, so I want to use the smtpTransport.
It just don’t work and gives no error messages/exeptions.

In the Settings.yaml of the site package I can feed the SwiftMailer configuration with any garbage you can imagine.
Inventing not existing Transports, Servernames, users …
…just can’t trigger any error message.

I’m shure my smtp settings (server, user, port …) are ok (tested with thunderbird).
I’ve spend hours with trial and error - without a result.

Also can’t get the LoggingTransport to work. By the way:
Documentation - Github - Swiftmailer says:

type: 'Neos\SwiftMailer\Transport\LoggingTransport'
and elsewhere I’ve found:
type: 'TYPO3\SwiftMailer\Transport\LoggingTransport'
The last reflects the path in the package.
None of them work.

I hope someone has some useful information for me, concerning:
the form preset, debugging SwiftMailer and the SmtpTransport.

Sending emails is such a basic task for a website. If you help me, I will write a short ducumentation on that.
I should be part of the base-Distribution imo, if the licence …

Have a nice Weekend