Best,
I was struggling a lot with Mageplaza extensions.
In this case it was Mageplaza smtp which needed a patch.
A lot of people were using Mageplaza SMTP as a free SMTP solution for magento 2.2
After updating to magento 2.3 it took a long time before Mageplaza had the module ready for Magento 2.3
Unfortunately it did not work at all even when they provided me the patch the module was not working.
After removing the module Mageplaza SMTP and running : php bin/magento setup:upgrade
An error occurred.
Module 'Mageplaza_Smtp':
Installing schema... Upgrading schema... SQLSTATE[42S21]: Column already exists: 1060 Duplicate column name 'sender'
How to resolve this issue?
SQLSTATE1060
Hoping for an answer Best regards and a happy 2019
EDIT: Solved by running composer remove mageplaza/module-smtp