Background Web-based interventions provide a possibility to enhance well-being in large groups of people. Only a few studies have studied the effectiveness of the interventions and there is no information on the sustainability of the effects. Study aims were to investigate both the short (2-month) and long-term (2-year) effects of email-based training for mental health and lifestyle. Methods Persons who completed an ‘Electronic Health Check’, as advertised in a TV program, were offered a chance to participate in email-based interventions. The baseline questionnaire was completed by 73 054 people, with 42 761 starting interventions, and 16 499 people participating in at least one of the follow-ups. Persons who did not choose to start the interventions served as controls. Results At baseline, the intervention group had a higher level of stress and lower gratitude and confidence in the future than the control group. Both groups showed improvement in the level of stress, but improvement was more marked in the intervention group (P
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