Internet marketers looking to increase their revenue via email should only send correspondence to those who have requested it, an expert in the field has advised.

Writing on DM News, Clint Smith suggests that gaining permission from users is the "first rule" of email marketing and could be vital in getting audience response and sustaining click-through rates.

Mr Smith added that marketers should also consider timing the delivery of their emails to when their intended audience are more likely to respond.

He warned against sending emails at the end of the working day or late on Friday afternoons.

Meanwhile, advertisers were warned that using phrases such as 'pills', 'single' and 'free' could see their messages be blocked by users' spam filters.

Ensuring content is easy-to-read by keeping emails short and avoiding too many pictures was also recommended.

According to Craig Spiezle, online safety director for Microsoft, many internet advertisers fail to check their email campaigns are being sent successfully as users look to block out increasing amounts of junk messages, reports Multichannel Merchant.