Thanks and this is getting very complex. If I understand this correctly (see * below) it is acceptable to send an email to a person at his or her work email address provided that it is for a product that is suitable for their business. If that is a good business practise or not is debatable. I might have that wrong so what I will do is get some professional advice tomorrow and post the answer here.
What a can of worms
What happens if I want to send marketing emails to business email addresses?
In simple terms, the Regulations do not apply to marketing emails sent to company employees (except employees at partnerships and sole traders), even if that email address incorporates the name of a living individual, and even if the email relates to goods or services that are for personal use.
If the email address identifies a living individual, you will instead need to comply with the Data Protection Act 1998. Amongst other things, this means that you would need to give recipients at business email addresses a right to optout of receiving any marketing from you, e.g.:
Please tick this box if you do not want to receive any marketing from us [] .
* By way of example, the Regulations would not apply if a marketing email was sent to John Smith, an account manager from an advertising agency, at his work address
[email protected]. The Regulations would, however, apply if a marketing email was sent to John Smith at his personal email address,
[email protected].
The opt-in and soft opt-in requirements in the CAP Code, on the other hand, apply to all individuals, irrespective of whether the marketing message is sent to their business account or their personal account. The opt-in and soft opt-in requirements do not, however, apply to marketing communications about business products that are sent to email accounts of company employees.
* For example, the CAP Code would apply if John Smith was sent a marketing email from a wine merchant, irrespective of whether that email was sent to his home or work email address, but not if a company sent a marketing email about software suitable for advertising agencies to John Smiths work account.
To achieve full legal and regulatory compliance, therefore, the stricter standard of the CAP Code should be adopted. In other words, if you are marketing products aimed at consumers, then you should always get the explicit consent of the proposed recipients of your emails unless you fall within the soft opt-in criteria. If you are intending to send marketing emails about business products to company employees only, you will not need explicit consent. However, as CAPs help note urges marketers to seek explicit consent from everyone before sending marketing emails, it is advisable to always use an opt-in box.
The only thing I would add is that are some newsletter services that charge a monthly fee and let you send newsletter from their website. This produces traceable click stats which essentially lets you know who is clicking what on the emails you are sending.
I'll boil it down 
