Febooti Command line email v4.1 is available now. Among updated OpenSSL libraries, we have made improvement related to iOS. One of our users have reported that iPhone uses CID image caching using CID from HTML email provided from email client. Checking relevant RFCs indeed confirmed, that image CIDs must be globally unique (unique in email itself is not enough). We switched to GUID, so chance of collision is almost impossible, even if all 7,000,000,000 of world population would send emails using our Command line email tool simultaneously.
Note to developers and users who use .eml files: If you develop similar software — that sends emails that can land in the iOS/iPhone inbox, then extra care should be taken, because if possible attacker can guess your next image CIDs, she/he can take advantage of that fact and poison iOS email client cache with some SPAM images that will appear in your sent HTML email message.