TMW will develop work to raise awareness of illegal minicabs and general safety advice. The emails will form part of a larger, integrated campaign that is set to break before Christmas.
This is the first time email marketing has been used in the Safer Travel campaign.
"We need to speak to people through the channels that they use when they plan their weekends and nights out, which is why online is a natural step to take," said Jason Cross, marketing manager at the Greater London Authority, which is responsible for TfL.
The Safer Travel at Night campaign is run in conjunction with the Mayor of London and the Metropolitan Police.
Last year, a location-based text service was launched to provide users with details of registered minicabs in their area when they sent the word 'HOME' to a short code. This service will remain the main call to action in the new campaign. Posters and station literature will also be used.
As part of the campaign, TfL is sending a mail pack to 40,000 students in London. It contains a letter from Mayor Ken Livingstone promoting safe travel, taxi information and maps.