In Spain, for example, article 21 of the LSSI as a rule prohibits advertising emails that the recipient did not request or expressly authorise beforehand. That covers a single message, not only mass mailings. The exception for an earlier contractual relationship has its own additional conditions, and calling a contact “B2B” does not create it.
Even where you may send the email, tracking it is a separate question with its own rules. Where rules that require consent apply, tracking may start only after that consent has been obtained. The link in the message lets the recipient withdraw consent later.
HawkOpen’s terms do not allow unsolicited bulk messaging and require that you have the authority to contact your recipients. Campaign emails carry an unsubscribe link and a one-click unsubscribe header. This answer does not cover US rules such as CAN-SPAM or UK rules.