An email-channel delivery can be very slow if the target population includes recipients with the Deco-mail email formats.
A recipient has a Deco-mail email format under either or both of the following cases:
To prevent this slow delivery, try the following:
Cleanse the target population so that it includes no Deco-mail recipient.
Design the containing workflow so that it excludes Deco-mail recipients from the target population.
Turn off Analysis for the automatic integration of images.
If the recipient has a Deco-mail email format, Campaign applies the typology rule - Analysis for the automatic integration of images. It turns image links in the email to the Deco-mail recipient into attachment image files. The total delivery size could grow quite huge and the throughput could slow down significantly.