When sending emails in bulk, there are 2 main types of authentication:
SpiceSend automatically adds default authentication to your marketing emails.
However, we suggest setting up custom domain authentication to remove the default SpiceSend authentication information ("via spicesend") that's displayed next to the sender's email address. Using custom authentication can improve your delivery rates.
SpiceSend's custom authentication process includes adding DKIM and SPF records from your SpiceSend account to your hosting site.
If you still experience problems, reach out to your domain provider's support site.