Thank you is not enough. Did IB give you discount on your commissions going forward? If no discount, any extra service? That is what matters
Do you mind sharing approximately how much commission you paid to IB to receive a thank you note?

Do you mind sharing approximately how much commission you paid to IB to receive a thank you note?
For the first time in 11 years, I received an email today from Interactive Brokers, thanking me for my business.
On this date 11 year(s) ago, you opened your account with Interactive Brokers.
Thank you for being a valued client!
Interactive Brokers Client Services
Hell has officially frozen over!