The short answer is "no," as Udit mentioned. However, mixing up the content type isn't something that I (and most Marketo users) would recommend doing, as:
- If you're using Recipient Time Zone functionality, it's supported only in streams with emails as content pieces; mixing emails with Default programs or having just the Default programs in the stream would hamper your ability to use the recipient time zone functionality within the Engagement program.
- Fundamentally, both the content types behave differently, i.e., Marketo won't send the email content in the nurture case if it's been previously sent (from any flow/campaign/program); however, Marketo will send the email from the Default program as long as the person isn't a member of it and it wasn't sent earlier from that engagement program only.
- If your default programs involve multiple filtering and complex logic, it might be harder to integrate them smoothly into an email-only content nurture stream.
Considering the above items. I'd vote for keeping things the way they are now, i.e., separate streams for email-only and Default program content pieces rather than mixing both in a single stream. Please let us know if you have any questions.
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