Maildoso SMTP mailboxes are designed for plain-text and light-HTML cold outreach. Outbound attachments (PDFs, images, documents) are not delivered — the message itself goes out, but the attachment is removed by our sending infrastructure. This applies to campaign emails sent through a sequencer and to messages sent from a mail app connected over SMTP.
Why
Attachments are one of the strongest spam signals for a cold email from a new sender, and they can't be scanned and rotated safely through a sending pool. Keeping attachments out protects the reputation of your domains and of the pool everyone sends from.
What to use instead
Host the file (Google Drive, Notion, your website, a document-sharing tool) and send a plain link. For cold email this also performs better than an attachment.
If you need to send a file to a prospect who has already replied, send it from your regular company mailbox rather than from a Maildoso outreach mailbox.
Replies and the Master Inbox
If you're replying from the Master Inbox or a connected mail app and an attachment isn't arriving, see Why aren't attachments being sent when I reply from a mailbox?
Not sure whether this applies to your setup? Contact us with the mailbox address and how you're sending (sequencer or mail app) and we'll confirm.