Outgoing emails not possible "Error 500: Can't send with empty from address"

[youri]

It is not possible for us to send emails from Espo. Either through compose or Reply to imported email. The log is attached below (with the to and from email addresses replaced with "valid@[from|to].address").
We use EspoCRM 5.2.5 with Advanced Pack 1.32.1 in the ACL Strict mode. Role has Data Privacy Permission set to 'yes', and Group Email Account Permission to 'all'.

[2018-06-13 12:28:09] Espo.ERROR: API [POST]:/:controller, Params:Array (     [controller] => Email ) ,
InputData:{"status":"Sending","isRead":true,"isImportant":false,"inTrash":false,"folderId":false,"isUsers":false,"isHtml":true,
"isSystem":false,"isJustSent":false,"assignedUsersIds":["5b0eb6ade9941ea7e"],"assignedUsersNames":{"5b0eb6ade9941ea7e":"Youri Tegelaers"},
"teamsIds":["5aa7b8ede8386bebe"],"teamsNames":{"5aa7b8ede8386bebe":"Support NL"},"attachmentsIds":[],"attachmentsNames":{},
"attachmentsTypes":{},"to":"valid@to.address","subject":"test outgoing","body":"<p>anything at all?</p>",
"bodyPlain":"anything at all?\n\n","from":"valid@from.address","cc":"","bcc":"","parentType":null,"parentName":null,"parentId":null,
"selectTemplateName":null,"selectTemplateId":null} - Can't send with empty from address. [] []
[2018-06-13 12:28:09] Espo.ERROR: Display Error: Can't send with empty from address., Code: 500 URL: /api/v1/Email [] []

[youri]

Related to one of our Workflows apparently, so not a Bug in itself, but just a weird feedback on something else.

[tanya]

What is in the action settings in from field? Could this field be empty in some case?