You need a gateway to send your emails. You can select your gateways from MailGun, SMTP, Brevo, Amazon SES, SparkPost, SendGrid, PostMark, Elastic Email and PepiPost.
Go to weMail→Settings→Email, you will find all the email gateways there. Just select any of the gateways with your API Key and go ahead with configuration.
Pick up your gateway to configure:
