dynect.net is a domain belonging to https://www.mywot.com/en/scorecard/dyn.com, which is used to support their email marketing services. Messages sent on behalf of Dyn's email marketing service may be sent through subdomains of dynect.net.
Most Dynect customers are probably legitimate. However, Dyn appears to send mail on behalf of https://www.mywot.com/en/scorecard/ynotmail.com, an email marketing business that apparently sends large quantities of unsolicited mail containing syndicated marketing links.
The domain is owned and operated by a trustworthy organisation.
However, this domain is also used for nameservers of websites not operated by Dyn so therefore content may exist on these servers that is abusive.
Dynamic DNS service used by MANY corporations and organizations. It does appear some companies are using it for email marketing trackbacks (greyhat spam, perhaps), but as the service is not free (and in fact is somewhat expensive) this is not a site that will be utilized by blackhat spammers and malware authors.