RE: Send Event Confirmation email without segment
> Does this mean segment is not necessary?
In general and most of situation, a customer journey will start with a segment(or marketing list members), but the start tile could also be a marketing form(inbound customer journey).
Above situations are working ways to send marketing email as far as I know.
> If we are running two customer journeys, one for the segment and the other for anyone who registered, will they receive two registration confirmation emails?
Yes, the first email will be triggered by marketing form, then when new contact record is added into segment(a period for recalculation), the second email will be sent.
But you can also build a segment which is based on behavior.(e.g: find contacts who submitted a specific form)
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https://docs.microsoft.com/en-us/dynamics365/marketing/segments-interaction
> What could be the behaviour if someone goes to event portal URL and registers for the event and not in segment (everyone doesn't necessarily register from the marketing form)
Like marketing form, the defaul event registration form could be also submitted by anyone, submitter will be created as a new contact record or just update its matching record, whatever he/she is existed in a segment.
You can enable "Captcha" and disable "allow anonymous registration"(only sign in user can submit form) to prevent spam registration.(the second option only works when event website is hosted on Portal)
But as far as I have tested, in this normal situation, you may still need a segment to send confirmation email.
Regards,
Clofly