Add webinar attendees to my newsletter?

[Josh77]

Ive gathered around 300+ emails from hosting a webinar (with registration). Cant find any info if I'm allowed to contact them further after the webinar like adding them to my newsletter. 

Have they agreed to receive marketing communications or not?

[Ray_Harwood]

Zoom won't restrict you from using the email addresses collected.  A one-time email thanking them for attending and inviting them to subscribe to your newsletter would not, in my opinion, be "marketing"... just good business practice.  Continuing to use their email addresses for further communication without opt-in permission isn't recommended.