The overall reputation for the IP address used was poor, although not listed in any blacklist and with a sender’s reputation of 71. The most detrimental item for the sender’s reputation in the past 7 days was hitting a spam trap.
The ESP the most affected by the spam issue is Outlook, with 100% of emails landing in spam.
The newsletter was experiencing an almost nonexistent open rate, and the transactional emails suffered from it with a decrease in open rate over the last 3 months.
The average daily volume of the client was 3500 emails/day, with a spike on Friday for the newsletter for 150K contacts. This spike in volume was always correlated with a negative spike in the open rate and click rate.
The issue is that the massive newsletter list causes a spike in the daily volume of Teo. This led ESP to believe such traffic was not usual practices and mark these emails are spam/not deliver them.