Configure your DNS
DNS records tell mail senders which service handles incoming email for the domain. They are usually set at the domain provider from which you acquired your domain.
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.