I've noticed that the subject in one of the spam emails looks like this in source:

```
Subject: Offe=?UTF-8?Q?=EF=BB=BF?=r fr=?UTF-8?Q?=EF=BB=BF?=om C=?UTF-8?Q?=EF=BB=BF?=redi=?UTF-8?Q?=EF=BB=BF?=t On=?UTF-8?Q?=EF=BB=BF?=e Ba=?UTF-8?Q?=EF=BB=BF?=nk=?UTF-8?Q?=EF=BB=BF?==?UTF-8?Q?=EF=BB=BF?=

```

but in web it looks normal

```
Offer from Credit One Bank

```

The only thing I recognize is `0xEF, 0xBB, 0xBF`, which is the UTF-8 BOM.

Which interpreter recognizes this character sequence `=?UTF-8?Q?=EF=BB=BF?=` ?

Is there a vulnerability around email subjects? What are they trying to do?