CKB:Mails can not be sent with enabled SPF
Aus Cryptshare Documentation
All mail servers with enabled SPF
If SPF (Sender Policy Framework) is enabled on your mail server, mails cannot be sent via Cryptshare.
As soon as SPF has been activated, mails will only be sent by mail servers that are explicitly enabled by the entry. If not, mails will be blocked. Because a mail sent via Cryptshare has several senders by default, the mail will be blocked.
Disable the setting Allow using individual sender addresses