Should I mail in my taxes after being rejected from e-file with the code IND-507 which is the first time it’s happened or look into it more before submitting again?

It depends on whether you have the right to claim the dependent in question. 

This rejection code means that another taxpayer has claimed a dependent listed on your return. This could be the dependent themselves, if they have income, another parent, a relative who thinks they can claim your dependent, or it could be a stranger. 

You aren't going to be able to e-file this year with this dependent. For example, if your teenage child filed a tax return and claimed themselves, you won't be able to e-file a return with them on it this year, even if they amend their return. 

So, your options are:

• Remove the dependent, and e-fie your return.
• Print and mail in your return with the dependent still on it.

If you claim a dependent that someone else claimed too, the IRS will decide who should to claim that dependent. If you have always claimed this dependent in the past, they are very likely to just accept that this is your dependent.

If it is not that clear, the IRS may ask you for more proof that this is your dependent.