It may be because you are running out of storage. You can check your current storage usage by following the instructions given in this article.
You can leverage MassMailer Utility to auto delete or manually delete some of your data storage and free up the space in Salesforce.
This would most likely resolve this issue. If you are still facing the issue, you can contact our support.
MassMailer Team
It may be because you are running out of storage. You can check your current storage usage by following the instructions given in this article.
You can leverage MassMailer Utility to auto delete or manually delete some of your data storage and free up the space in Salesforce.
This would most likely resolve this issue. If you are still facing the issue, you can contact our support.