Sending emails without permission can be illegal, depending on the circumstances. Generally, if you send unsolicited commercial emails, also known as spam, without the recipient's consent, it is considered illegal under various anti-spam laws.
These laws differ from country to country, but most have similar requirements for commercial emails, such as the requirement to include an opt-out mechanism and to identify the sender.
In the United States, the CAN-SPAM Act sets guidelines for commercial emails, which include requirements to provide a clear and conspicuous opt-out mechanism, include accurate header and subject lines, and include the sender's physical address. Violating the CAN-SPAM Act can result in penalties of up to $42,530 per email.
In addition to the legal consequences, sending unsolicited emails can damage your reputation and harm your business. It is always best to obtain permission from recipients before sending them any commercial emails, to ensure that you are complying with applicable laws and maintaining good business practices.