Configure your DNS
DNS records tell mail senders which service handles emails for a domain. They are usually set at the domain provider from which you acquired your domain name.
Here are somes DNS guides which might help you:
Try with an empty field instead, or with your domain name.
put the lowest value allowed (could be 1 or 10 for instance).
Set the MX record
Login to your domain provider, delete any existing MX records in the DNS editor, and add this one.
Host / Name Value Priority @ mail.postale.io. 0
Add 3 TXT records
Delete any existing TXT records for SPF, DMARC, and DKIM, and add these three. They will help your emails avoid SPAM folders.
Please specify a domain for DKIM and DMARC:
Host / Name Value @ v=spf1 mx ~all
Add 2 CNAME records
Those records make mail clients (Outlook, Thunderbird, ...) autoconfigure themselves from your credentials.
Host / Name Value autoconfig mail.postale.io. autodiscover mail.postale.io.