[Tickets #15019] IMP creates email with empty to field

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Ticket URL: https://bugs.horde.org/ticket/15019
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  Ticket             | 15019
  Created By         | o+horde at immerda.ch
  Summary            | IMP creates email with empty to field
  Queue              | IMP
  Version            | Git master
  Type               | Bug
  State              | Unconfirmed
  Priority           | 2. Medium
  Milestone          |
  Patch              |
  Owners             |
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o+horde at immerda.ch (2020-07-06 09:18) wrote:

When the user provides only bcc recipients, then imp creates a mail  
with an empty "to: " header, ie. it adds the header with an empty  
header body field.

Apparently this is not compliant with RFC 4322, which defines the  
syntax of the header as follows:

to              =   "To:" address-list CRLF
address-list    =   (address *("," address)) / obs-addr-list

where the address-list has to contain at least one address. For an  
empty to: the mua is supposed to generate a message without to.

we believe that this issue is currently causing the affected emails to  
be rejected by gmx/web.de